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About the Author Debbie Routh is an experienced junior high Life Science teacher. Debbie has 18 years of teaching experience, including Biological Sciences, Earth Science, Health, Geography, Resource, and Physical Education. She is a member of the National Science Teachers Association and has co-planned with other teachers science curriculum for grades K–12. Learning About DNA By Debbie Routh COPYRIGHT © 2003 Mark Twain Media, Inc. ISBN 978-1-58037-788-1 Printing No. 1577-EB Mark Twain Media, Inc., Publishers Distributed by Carson-Dellosa Publishing Company, Inc. The purchase of this book entitles the buyer to reproduce the student pages for classroom use only. Other permissions may be obtained by writing Mark Twain Media, Inc., Publishers. All rights reserved. Printed in the United States of America. Learning About DNA Table of Contents Table of Contents Introduction................................................................................................................................ 1 What Is DNA?............................................................................................................................ 2 The History of DNA................................................................................................................... 4 Learning About Microscopes..................................................................................................... 6 Microscope parts and functions........................................................................................ 7 How to Use a Microscope: Student Lab.................................................................................... 9 The Cell................................................................................................................................... 12 Cell Organization..................................................................................................................... 14 I’m Made of These?: Student Lab............................................................................................ 18 Mitosis..................................................................................................................................... 21 Meiosis.................................................................................................................................... 22 “Cell-a-bration Day”: Cell model project.................................................................................. 24 You Are What You Inherit......................................................................................................... 25 What Are Dominant and Recessive Traits?............................................................................. 27 Dominant and Recessive Traits in Humans............................................................................. 30 FYI: Common Mendelian Traits................................................................................................ 31 Predicting Heredity.................................................................................................................. 32 How Does DNA Work?............................................................................................................ 35 Modeling the Structure of DNA................................................................................................ 38 Some DNA to Study: DNA Research Project.......................................................................... 39 DNA Vocabulary List................................................................................................................ 40 DNA Crossword Puzzle........................................................................................................... 41 DNA Unit Test.......................................................................................................................... 42 Answer Keys............................................................................................................................ 44 Bibliography............................................................................................................................. 46 © Mark Twain Media, Inc., Publishers ii Learning About DNA Introduction Introduction Welcome to the exciting world of genetics (juh NET iks), which is the study of traits and how they are passed on from parent to offspring. In this book, you will learn many things about DNA, chromosomes, genes, the cell, and all of the components of heredity. Has anyone ever told you that you have your mother’s eyes or your father’s smile? What did they mean by that? After all, these are your eyes and smile, right? What they meant by this remark is that you have close similarities to your parents. All offspring resemble their parents because they inherit traits or characteristics from them. In this book, you will learn the reasons why. This book will help you to understand concepts such as your genes, dominant and recessive traits, what a chromosome is, how to predict heredity, and how environmental factors may affect the traits of plants and animals. Of course, we will also have to learn about cells, the building blocks of life. That is where your DNA is located. But you cannot learn about DNA located within the cell without some understanding of the microscope. A microscope is a necessary tool used by scientists to study the smallest unit of life. Student observers will use many scientific process skills to discover the world of DNA. The student reinforcement worksheets that serve as a follow-up activity for each lesson contain at least one higher-level thinking question. So come on, student observers, put on those thinking caps and use your process skills to observe, analyze, debate, design, and report. This unit contains a variety of lessons that will help you practice scientific processes as you make new, exciting discoveries about genetics and the secret code of life called DNA. Teacher note: This book supports the National Science Education Standards and is designed to supplement your existing science curriculum. Each lesson opens with a manageable amount of text for the student to read. The succeeding pages contain exercises and illustrations that are varied and plentiful. Phonetic spellings and simple definitions for terms are also included to assist the student. The lessons may be used as a complete unit for the entire class or as supplemental material for the reluctant learner. The tone of the book is informal; a dialogue is established between the book and the student. © Mark Twain Media, Inc., Publishers Learning About DNA What Is DNA? What Is DNA? DNA is the thread of life. In each of the cells that make up your body, information is stored in the form of DNA. This information is the genetic blueprint that contains all of the directions that control the functions of your body. The differences in the information stored are responsible for all of the inherited differences among people. The cells in your body have stored a great deal of information in a very small space. They can even make an exact copy of the DNA to be passed on to new cells produced by your body. So what exactly is this thing called DNA? It’s a complex chemical substance found in the cell’s nucleus. This large organic molecule is called Deoxyribonucleic (dee OK see RY boh noo KLEE ik) Acid. Scientists studied cells for many years before they discovered the structures within the cells called chromosomes. The chromosomes contain coiled and fixed genes. They consist of two strands connected by base pairs like a twisted zipper. Each individual has a unique genetic makeup. The Shape of DNA DNA is like a miniature ladder with two sides and rungs connecting the sides. The sides twist around each other like a spiral staircase with ten rungs for each turn. DNA Make-up DNA is made up of three substances, all connected together in a definite pattern. • Phosphate (P) • Deoxyribose (D) - a sugar • 4 bases - There are four nitrogen bases present in DNA: adenine (A), cytosine (C), guanine (G), and thymine (T). The Sides or Strands of the Ladder—The Backbone Imagine if you can, that each side of the ladder is made up of phosphates (P), joined with units of deoxyribose (D). The units alternate to form the two strands. Side 1: P-D-P-D-P-D-P-D-P-D-P-D-P-D-P-D-P-D-P-D-P-D-P-D- Side 2: P-D-P-D-P-D-P-D-P-D-P-D-P-D-P-D-P-D-P-D-P-D-P-D- Rungs of the Ladder—The Base Pairs Now try to visualize the two strands connected by pairs of bases. Each base pair forms a rung on the ladder. The four bases will only pair up with each other in an orderly manner. Adenine (A) pairs only with thymine (T), and cytosine (C) only pairs with guanine (G). A single Dna molecule, or ladder, can have thousands of steps. The number of steps and how they are arranged form a genetic code. The genetic code determines the different kinds of inherited traits. Genetic Code: P-D-P-D-P-D-P-D-P-D-P-D-P-D-P-D-P A T C G A G T C T A G C T C A G P-D-P-D-P-D-P-D-P-D-P-D-P-D-P-D-P © Mark Twain Media, Inc., Publishers Learning About DNA What Is DNA?: Reinforcement Activity Name: Date: What Is DNA?: Reinforcement Activity To the student observer: What is responsible for the differences in people? Analyze: What would two developing embryos that contained the same genetic code look like? Directions: Answer the following questions about a DNA molecule. 1. What is DNA? 2. What does DNA look like? 3. What substances make up a DNA molecule? 4. What is the backbone (sides) of the DNA ladder made of? 5. What are the rungs (steps) of a DNA molecule made of? 6. What are the four nitrogen bases present in DNA, and how do they pair up? © Mark Twain Media, Inc., Publishers Learning About DNA The History of DNA The History of DNA Since the 1800s, it has been known that the nuclei of cells contained a chemical called nucleic acid. People have always noticed that certain traits are passed on from one generation to the next. In 1857, an Austrian monk, Gregor Mendel, was the first person to describe how these traits called genes are inherited. Mendel studied ordinary pea plants for eight years. The pea plants made an excellent choice for experimentation because they grew and reproduced quickly. He was able, in a relatively short period of time, to observe nine generations of the pea plants. He observed a variety of traits in them, such as tallness or shortness, the color green or yellow, smooth or wrinkled seed coats, and so on. Mendel wondered why certain traits of the parents showed up, while others did not. He used a branch of mathematics called Gregor Mendel probability to predict what kind of plants would be produced from each parent. His research led to the principles of genetics and his title, the “Father of Genetics.” In 1928, a taxonomist named Frederick Griffith, who classified pathogens (disease-causing organisms), showed the existence of an inheritance molecule. He performed a remarkable experiment with a bacterium called Streptococcus pneumonia. He observed that these bacteria produced two types of colonies on the growth—medium-rough and smooth. It was known by this time that chromosomes contained both protein and DNA. Scientists wondered: upon which of these components was the heredity information written? Did the hereditary information come from the protein or the DNA? Griffith then used mice to conduct an experiment to test this question. He removed the protein capsule and injected mice with only the DNA; the mice died. He also discovered the one strain, smooth (S), was deadly while the other strain, rough (R), was harmless. He heated the (S) bacteria and found it to be harmless, as the mice did not develop the disease. He then injected the mice with the harmless (R) strain and found that the mice did not develop the deadly disease. However, when he injected the mice with both the heated harmless (S) strain and the harmless (R) strain, the mice all caught a raging case of the disease and died. Griffith realized the (R) bacteria had transformed into a harmful strain, and the change became an inherited permanent change, thus proving the existence of an inherited molecule. In 1944, Oswald Avery continued the work of Griffith and identified DNA as the inheritance molecule. Most scientists believed that protein had to be the substance that carried hereditary material. They believed that DNA was not complex enough to carry out such a task. Avery grew huge amounts of deadly bacteria in vats of broth that were heated to the temperature of human blood. He then spun the broth in a centrifuge to separate the pneumococci. He broke open the cells to extract fluid and began testing them one by one. This took years, and none of the proteins Avery tried affected the pneumococci. Only a non-protein substance could induce a smooth, deadly coat in harmless pneumococci. Analysis of the non-protein substance found a 1.67:1 ratio of nitrogen to phosphorous. As it happened, this was the same ratio found in DNA. Avery felt certain he had made a mistake. He added enzymes to the DNA transforming © Mark Twain Media, Inc., Publishers Learning About DNA The History of DNA The History of DNA (cont.) agent, knowing it would digest any protein present. Avery then introduced the resulting product to the harmless (R) strain, and the smooth coat appeared. Avery then became convinced that DNA was, in fact, the inheritance molecule. Avery became the world’s first genetic engineer by introducing a gene into an organism that did not previously have that gene. In 1951, Rosalind Franklin discovered the double-helix shape of DNA. She discovered that the DNA molecule was really a strand of molecules in a spiral form. By using an X-ray technique, she was able to show that the spiral was actually two spirals, similar to a spiral staircase. In 1953, James Watson and Francis Crick made a model of the DNA molecule. The model was accurate and has changed very little since then. According to Watson and Crick, the sides are made up of two twisted strands of sugar and phosphate molecules. The stairs that hold the strands apart are made up of molecules called nitrogen bases. The DNA molecule is made up of five elements: carbon, hydrogen, oxygen, nitrogen, and phosphorus. Francis Crick and James Watson © Mark Twain Media, Inc., Publishers Learning About DNA Learning About Microscopes Learning About Microscopes Before we can observe and study cells, we must learn to use a very important scientific tool, the microscope. Micro means “very small,” while scope means “to look at.” Over time, scientists developed a tool to make things look larger than their actual size. Microscopes use lenses (curved pieces of glass) to bend light rays in order to make an enlarged image. The first compound microscope was invented around 1590 by two Dutch eyeglass makers, Hans and Zacharias Janssen. Their microscope had two lenses, one at each end of a tube, but the lenses were poor; as a result, the images produced were blurred and distorted. It wasn’t until 1670 that the quality of the lenses had improved enough to produce a clear image. Kinds of Microscopes There are many different kinds of microscopes. Microscopes are either simple (containing one lens) or compound (containing two or more lenses). A simple microscope is like a magnifying glass. Have you ever used a hand lens before? If you have, you have used a simple microscope. Light microscopes use light and lenses to magnify (enlarge) things. The microscopes you use in your classroom are compound light microscopes. They let light pass through the object and then through two or more lenses. Convex lenses are used as magnifying lenses and bend the light toward your eye. They usually have an eyepiece lens with the power to magnify something ten times. The objective lenses vary in power. Using the different objective lenses changes the magnification of the microscope. The low-power objective is usually a 10X magnification lens. It shows more of the object but less detail. The high-power objective contains the lens with the greatest amount of magnification. It shows less of the object you are viewing but shows it in greater detail. The magnification power of a microscope is the product of the magnifying power of the lenses: take the magnification of the eyepiece and multiply it by the magnification of the objective (nosepiece) lens to determine the total magnification of the microscope. A standard microscope can make objects appear 50 to 500 times larger than their actual size. Magnification of a Microscope Eyepiece lens = 10X (magnification) Objective lens = 43X (magnification) Total magnification = 430X (the product of 10 x 43) Electron microscopes use electrons to magnify objects; this type of microscope does not use light. Electrons are the particles that light up your television screen. Scientists use electron microscopes to look at things too small to be seen with a light compound microscope. The transmission electron microscope (TEM) is used to study parts inside a living cell. The scanning electron microscope (SEM) is used to view dead cells and tissue. It is also used to see the surfaces of the whole object. These microscopes are very expensive and are not likely to be found in your classroom. They are used in research centers, hospitals, and doctors’ offices. Electron microscopes can magnify objects 300,000 times their actual size. Your classroom may have a light stereoscope microscope; this type of microscope is used to see three-dimensional views of objects too thick to let light pass through. For example, if you wanted to see a worm up close, you would use one of these microscopes. © Mark Twain Media, Inc., Publishers Learning About DNA Microscope Parts and Functions Microscope Parts and Functions Microscopes are fun and easy to use if you know their parts and what they do. All compound microscopes have the same basic parts. As you read about the parts of the microscope, locate each in the drawing below. • Eyepiece - contains the lens you look through; the top part of the microscope • Body tube - the hollow tube through which light passes; also maintains the correct distance between the lenses • Nosepiece - holds the objective lenses and rotates to change the magnification • Objective lens - several objective lenses, each having a different magnification • Stage - supports the object (microscope slide) being viewed • Stage clips - used to hold the microscope slide in place • Diaphragm (DY uh fram) - changes the amount of light that enters the body tube • Mirror or light source - used to send light up through the hole in the stage, the object, and the lenses • Base - supports the microscope and is used to carry it; the bottom part of the microscope • Arm - supports the body tube and is used to carry the microscope • Fine adjustment knob - moves slightly to sharpen the image while focusing • Coarse adjustment knob - turns to raise and lower the body tube or stage for focusing (Always use this knob first.) Eyepiece Coarse adjustment knob Body tube Nosepiece Fine adjustment knob Objective lenses Arm Stage Stage clips Diaphragm Mirror or light source Base Note: Always use both hands to carry a microscope. One hand should be on the arm, and the other hand should be under the base. Always store your microscope with the low-power objective in place. When focusing your microscope, use the low-power objective first. © Mark Twain Media, Inc., Publishers Learning About DNA Learning About Microscopes: Reinforcement Activity Name: Date: Learning About Microscopes: Reinforcement Activity To the student observer: Can you explain the proper way to carry a microscope? Analyze: How does changing the objective lens from low to high power affect the image of the object you are viewing (How does it change what you see in the microscope?)? Directions: Answer the following questions. 1. What makes microscopes compound or simple? 2. Upon which part of the microscope do you place the object you are viewing? 3. Who invented the first compound microscope? 4. If the eyepiece of the microscope has a 10X lens, and the high objective has a 50X lens, what is the total magnification in high power? 5. Which parts enable you to adjust the focus of the microscope? With which part should you focus first? 6. When would you use an electron microscope? 7. When would you use a stereoscope microscope? © Mark Twain Media, Inc., Publishers Learning About DNA How to Use a Microscope: Student Lab Name: Date: How to Use a Microscope: Student Lab To the student observer: Microscopes enable us to see things we cannot see with our eyes alone. In this lab, you will learn how to use a microscope by becoming familiar with its parts. You will also learn how to prepare objects for viewing. In this experiment, you will look first at a very small, lowercase letter “e” cut from a magazine or even from this sheet. Using the lowercase letter “e” will help you understand how a microscope works and how the lens system changes the position of the object you are viewing. Be patient, and have fun while you explore the world of the microscope. Materials needed: (Note: Teachers may obtain threads by pulling the threads off the edges of cut pieces of nylon and wool fabric.) Microscope Scissors Dropper Strand of hair Magazine Cover slip Microscope slide Nylon thread Water Wool thread Part A: Procedure 1. With a partner, study the figures below, and identify the parts of your microscope so you will understand the directions in this lab. 2. Cut a small (the smaller, the better) lowercase letter e from a magazine, and place it on a slide. Put a drop of water on the slide next to the letter, and place a cover slip over both the water and the letter. 3. Place the slide on the microscope stage. Move the slide to center the e over the hole in the stage. Use stage clips to hold the slide in place (You may have to move it slightly in one direction or the other to bring it into your field of view. The field of view is the circle you see when looking through the microscope.). 4.Turn on the light if your microscope has one. If it does not have a light, adjust the mirror so that the light is reflected through the eyepiece. 5. Note the position (how it is sitting) of the letter e on the slide without looking through the eyepiece. Is the letter sitting right-side-up, upside-down, sideways, etc.? In the Data and Observation portion of this lab, draw a picture of the letter e as it looks on the microscope slide. Light Source Microscope using a light source (angled body tube) © Mark Twain Media, Inc., Publishers Microscope with a mirror (straight body tube) Learning About DNA How to Use a Microscope: Student Lab Name: Date: How to Use a Microscope: Student Lab (cont.) 6. Now it is time to check your objectives on the revolving nosepiece. Click the low-power objective (usually 10X) lens in place. The low-power objective is the shortest one. The lens should be directly over the hole in the stage. Turn the coarse adjustment knob to bring the lens close to the slide. The low-power lens is short enough, so you shouldn’t hit or break the slide or damage the lens. 7.Everything is now ready for you to look through the eyepiece and begin to practice focusing by slowly turning the coarse adjustment knob. Remember, if you cannot see the letter, you may have to move the slide slightly to make sure the letter is under the lens. 8. When the letter is clearly visible, draw what you see in your field of view (through the eyepiece) in the data and observation portion of this lab. Discuss with your partner what you have observed about the position of the letter. 9. When the letter is clearly in view, move the slide to the left while looking through the eyepiece. Which way did it appear to move? Next, with the letter in view, move the slide to the right. Which way did it appear to move? Discuss with your partner what you have just observed. Part B: Preparing microscope slides for viewing 1. Place a drop of water on a clean glass slide. Put a strand of your hair on the drop of water and place a cover slip on top. 2.Observe the hair, using the same procedure you used in Part A. 3.Observe the wool and nylon threads next, using the same procedure. Data and Observations: 1. In the spaces below, draw what you observed about the letter e during your lab activity. Without the microscope Through the microscope a. Position of the letter e b. Position of the letter e (in field of view) 2. In the spaces below, draw what you observed in your field of view when looking at the strand of your hair and the nylon and wool threads during your lab activity. a. hair © Mark Twain Media, Inc., Publishers b. nylon thread 10 c. wool thread Learning About DNA How to Use a Microscope: Reinforcement Activity Name: Date: How to Use a Microscope: Reinforcement Activity 1. Compare your drawing of the letter e without the microscope to the drawing of the letter as seen through the microscope. Note below how the microscope changed the position of the letter. 2. What direction does the object appear to move into your field of view when compared to the way you actually moved it? 3. Describe the difference you observed in the field of view between the two kinds of threads. 4. Describe how to prepare a slide for viewing. 5. Why do you think it’s a good idea to always focus with the low-power objective in place first? 6. Which adjustment knob should you focus with first? 7. What is the magnification of your power objectives? High Low 8. Do you know how to calculate the total magnification of the microscope you used today? Write the procedure below. © Mark Twain Media, Inc., Publishers 11 Learning About DNA The Cell The Cell Observers, we need to take care of some business before we continue our study of DNA. We can’t begin to understand what DNA is or how heredity works without understanding the cell. So, let’s back up for a moment and take a look at cells. A brick building is made up of many bricks, which are its basic units of structure. Cells are like the bricks of a building; they are the building blocks of all living things. All living things are made up of one or many cells. Plants and animals are made up of many cells, while some living things consist of only a single cell. The human body has over ten trillion cells. Cells, the smallest units of life, are the basic units of structure and function of all living things. Discovery The first person to see cells was an English scientist, Robert Hooke. He used a simple compound microscope (a microscope with more than one lens), to view thin slices of cork. Cork is found in some plants. The first cells Hooke saw were dead cells that seemed to resemble many small boxes. The small boxes reminded Hooke of the rooms monks slept in—these rooms were called cells. So, Hooke decided to also name the structures that made up the cork cells. Anton van Leeuwenhoek (AN tun van LAY vun hook) was the first person to observe living cells. He observed single-celled organisms in a drop of pond water. He used a simple microscope that he had made, using a tiny glass bead for a lens. The Cell Theory By the 1800s, better microscopes were being made, and scientists had many ideas about cells. Their ideas were put together into a theory, an idea that is consistently supported by data. The credit for the theory goes to two German scientists, Matthias Schleiden, a botanist (one who studies plants), and Theodor Schwann, a zoologist (one who studies animals). Schleiden discovered that plants were made up of cells, and Schwann reported the same to be true of animals. Together, they hypothesized that all living things were made up of cells. Rudolph Verchow, a German doctor, hypothesized 15 years later that cells didn’t just form on their own. He believed that cells divided from an existing cell to form new cells. This discovery led to the third part of the cell theory. The cell theory is one of the major theories in science. It is not based on the hypotheses and observations of only one scientist, but is the result of the discoveries of many scientists. Today, the Cell Theory serves as the basis upon which histologists (scientists who study cells) have built their ongoing explosion of knowledge and information in cell biology. The cell theory states that: • All organisms are made up of one or many cells; • Cells are the basic unit of structure and function in all organisms; and • All cells come from other cells that already exist. © Mark Twain Media, Inc., Publishers 12 Learning About DNA The Cell: Reinforcement Activity Name: Date: The Cell: Reinforcement Activity To the student observer: Why is it important to study the cell in order to learn about DNA? Analyze: What is the relationship between the improved microscope and the discoveries made by scientists about cells? Directions: Complete the following sentences. 1. are the building blocks of all living things. 2. was the first person to see cells. 3.The first cells observed were cells in thin slices of cork. 4. was the first person to observe cells in a drop of pond water. 5.The is one of the major theories in science. 6.The work of , , and led to the development of the Cell Theory. 7. are scientists who study cells. 8. List the three parts of the Cell Theory: a. b. c. © Mark Twain Media, Inc., Publishers 13 Learning About DNA Cell Organization Cell Organization Structure and Function Cells have several things in common and come in two basic types. They all have a membrane, a gel-like material called cytoplasm inside the membrane, and a nucleus that controls or directs the cell. The cytoplasm contains proteins, nutrients, and all of the other cell organelles (structures). The control center is either a nucleus or nuclear material. The two basic types of cells are eukaryotic (with a true nucleus) and prokaryotic (no true nucleus). Eukaryotic cells have a nucleus surrounded by a membrane. DNA is located in this part of the cell, which is the reason the nucleus is often called the control center of the cell. most cells are eukaryotic. Prokaryotic cells have nuclear material floating around inside the cytoplasm but lack a nuclear membrane. Bacteria, the simplest cells in existence, are prokaryotic. Two kinds of cells: Eukaryotic Cell • Eukaryotic - a cell with a true nucleus; nuclear material is inside a membrane. • Prokaryotic - a cell without a true nucleus; nuclear material is present, but it is not inside a membrane (i.e., bacteria). Prokaryotic Cell The three main parts of a cell: * Cell membrane - A thin layer that encloses the cell and controls the movement of materials into and out of the cell; it offers shape and protection for the cell. * Nucleus - Round or egg-shaped structure found near the center of the cell and is usually darker in color; contains DNA and controls all cell activities. * Cytoplasm - All the living material in a cell except the nucleus; contains proteins, nutrients, and all of the other cell organelles. plant cell Animal cell Nucleus Cell membrane Cytoplasm © Mark Twain Media, Inc., Publishers 14 Learning About DNA Cell Organization: Reinforcement Activity 1 Name: Date: Cell Organization: Reinforcement Activity 1 To the student observer: A membrane surrounds the nucleus of a cell. Based on what you have learned, what do you think the job of a nuclear membrane would be? Analyze: In your opinion, what do you think would happen to a cell if the nucleus was taken out of it? Directions: Answer the following questions. 1. What controls the activities of a cell? 2. List the three functions of the cell membrane. a. b. c. 3. List and explain the two types of cells. a. b. 4. A cell is mostly made up of what substance? 5. Label the three main parts of the cell in the diagram below. A. B. C. © Mark Twain Media, Inc., Publishers 15 Learning About DNA Cell Organization Cell Organization (cont.) The Other Cell Parts A cell is a remarkable miniaturization of life’s functions. A cell moves, reacts, protects itself, grows, and even reproduces. It has a control center, power plants, internal communication, and construction and manufacturing elements. Cells come in many sizes, shapes, and textures. Cells are classified into four categories. Associated plant cells live in communities in association with each other to form the multi-cellular organisms that make their own food. Plant cells are more rigid and contain a nonliving structure called a cell wall and green disc-shaped parts called chloroplasts. The chloroplast allows the plant to make its own food. Plant cells are more square or rectangular in shape. Associated animal cells also live in communities in association with one another to form multi-cellular organisms that move about in order to obtain food. Animal cells do not contain chloroplasts or a cell wall. Free-living animal cells form single-celled animal-like organisms. Free-living plant cells form single-celled plant-like organisms. Going About Business—Organelles in the Cell’s Cytoplasm Observers, now that you know what the three main parts of the cell are, let’s take a closer look at the cell. A cell can be compared to a factory. There are many machines in a factory, and each performs a certain task. It takes all of the machines working together to run the factory. Organelles (the machines of the cell—parts that float in the cytoplasm) are responsible for keeping the cell alive and working properly. Here’s a look at the organelles of that microscopic blob of jelly called a cell. The energy to keep the cell working is produced in sausage-shaped structures called mitochondria (MYT uh KAHN dree uh). The food obtained or produced in the cell is burned in a chemical operation to release energy. The mitochondria are often called the “powerhouses” of the cell. The vacuoles (VAK yoo wohls), another cell organelle, are liquid-filled spaces that serve as storage bins. They store food, water, and waste for the cell. Golgi (GOL jee) bodies, protein-filled sacs, store and package the protein that the cell exports. When the protein is shipped out, bits of the Golgi bodies break off, and the protein is neatly packaged and ready for market. Ribosomes work under the direction of the nucleus to make the protein. Proteins are the building materials of the cell. Ribosomes are often found along the edge of a transferand-delivery setup known as endoplasmic reticulum (EN doh PLAS mik ri TIK yoo lum), or ER. ER is actually a network of tubes that makes up the transport system for the cell. Animal cell Mitochondria plant cell Nucleus Mitochondria Chloroplast Cell membrane Cell wall Cytoplasm Ribosomes © Mark Twain Media, Inc., Publishers Golgi bodies Endoplasmic reticulum 16 Vacuole Ribosomes Learning About DNA Cell Organization: Reinforcement Activity 2 Name: Date: Cell Organization: Reinforcement Activity 2 Parts of Animal and Plant Cells To the student observer: Explain what cell organelles are. Analyze: Why does a cell need energy? In your opinion, which cells contain more mitochondria: your skin cells or your muscle cells? Directions: Answer the following questions. 1. Why are cells often compared to a factory? 2. List the three functions of the cell membrane. a. b. c. 3. What are the four categories of cells? a. b. c. d. 4. Label the cell parts and organelles in each cell below. Use the following terms: Cell Membrane, Cell Wall, Chloroplast, Cytoplasm, Endoplasmic Reticulum, Golgi Bodies, Mitochondria, Nucleus, Ribosomes, Vacuole. plant cell Animal cell B. A. C. J. D. E. I. F. G. J. H. © Mark Twain Media, Inc., Publishers A. 17 Learning About DNA I’m Made of These?: Student Lab Name: Date: I’m Made of These?: Student Lab No fooling, observers; you really are made up of many small units called cells. Just in case you have ever wondered what a cell looks like, let’s take a look at animal and plant cells under the microscope. In this lab, you will learn and practice how to prepare things for viewing under a microscope. You will see the tiny individual cells (units) of which each living thing is made. You will also have the opportunity to compare animal cells to plant cells. Materials: Onion Elodea (an aquarium plant) Slides and cover slips Microscope Needle 2 eyedroppers—one for water and one for staining solution Water Iodine stain or blue staining solution in a small beaker or container Toothpicks or prepared cheek cell slides Procedure for observing plant cells Onion cells and elodea leaf cells: 1.Obtain a small piece of onion and a green elodea leaf from your teacher. 2. Place the elodea leaf on the microscope slide and add a drop of water. Cover with cover slip. 3.Use a needle to peel a thin, clear piece of tissue from the inside section of an onion. 4. Place the onion tissue on the microscope slide. Try to avoid having any wrinkles in the tissue. 5. Add a drop of staining solution to the onion tissue and cover with a cover slip. (The stain helps to better reveal the clear tissue’s individual cells.) 6. View the onion and elodea under the microscope. Use low-power objectives for magnification. Then, taking care not to damage the lens or break the slide, view under high power. 7. Many small cells should be observed. 8. Draw what you observed in the field of view. Onion Cells Low Power © Mark Twain Media, Inc., Publishers High Power 18 Elodea Leaf Cells Low Power High Power Learning About DNA I’m Made of These?: Student Lab Name: Date: I’m Made of These?: Student Lab (cont.) Procedure for observing animal cells Cheek Cell: 1. Add a drop of staining solution to the center of a clean slide. 2. With the end of a clean toothpick, gently scrape the inside lining of your cheek. Stir the toothpick in the staining solution. Note: You will not see anything in the staining solution 3. Place a cover slip over the drop of staining solution. View under low power and then, with care, under high power. 4. Many small cells should be observed. They will be more rounded in appearance than plant cells. 5.If your teacher has already prepared slides of cheek cells for you to view, you may skip the first two steps. Students sometimes have difficulty making their own cheek cell slides, and prepared slides save a great deal of time. 6. Draw what you observed in the field of view below. Cheek Cells Low Power High Power Strategy Check: Do you agree with the idea that living things are all made up of cells? Can you prepare and observe cells under the microscope? Could you see differences between plant and animal cells? Can you label the cells below correctly? Cheek Cell Elodea Cell B. A. C. D. E. © Mark Twain Media, Inc., Publishers F. 19 Learning About DNA Prove You Can: Reinforcement Activity Name: Date: Prove You Can: Reinforcement Activity Part A: To the student observer: Mark each column below with a check mark (✔) for the cell or cells the words or phrases describe. More than one choice may be used for some words and phrases. The first one has been done for you. Description 1. rectangular or brick-like shape Onion Elodea ✔ Cheek ✔ 2. chloroplasts 3. nucleus 4. round or circular in shape 5. cell wall 6. cytoplasm 7. no cell wall 8. animal cell 9. plant cell 10. cell membrane Part B: Analyze: Can you relate the parts of the cell to your school? Match each cell part function with the corresponding school area or part. 1. Cell wall a. Supply or storage room 2. Vacuole b. Doors and windows 3. Chloroplast c. Principal’s office 4. Nucleus d. Bricks of the building 5. Cell membrane e. Cafeteria Part C: Predict: What if you were to look at a piece of tomato skin under the microscope? What would you see? © Mark Twain Media, Inc., Publishers 20 Learning About DNA Mitosis Mitosis All living things grow and repair themselves by reproducing cells in a process called mitosis. In order to reproduce a cell, everything inside the cell must first be duplicated (copied). Mitosis is the process by which a cell divides. Cells divide in two steps: the nucleus of the cell divides first, and then the cytoplasm divides to form two daughter cells. During cell division, DNA breaks into short pieces called chromosomes; each organism has a specific number of chromosomes. For example, every body cell in fruit flies has eight chromosomes, or four pairs. All chromosomes are found in pairs. You have 46 chromosomes (23 pairs) in all of your body cells. Two of those chromosomes determine your gender. The others carry information, such as your height, eye color, and so on. Mitosis can be broken down into five steps. This process produces only body cells, not gametes (reproductive cells—eggs and sperm); they are produced by the process of meiosis, which is described on the next page. The Five Steps of Mitosis: Step 1: Interphase - DNA breaks up into short chromosomes. Each chromosome makes an exact copy of itself. Each pair stays attached in the middle (the centromere). Step 2: Prophase - Chromosomes become visible; the nuclear membrane disappears. Two small structures move to opposite ends of the cell, stretching threadlike spindle fibers across the cells. Step 3: Metaphase - Chromosomes line up along the middle (the center of the cell, and each centromere attaches to a spindle fiber). Step 4: Anaphase - Spindle fibers go to work like tugboats, pulling each pair apart toward opposite ends of the cell. Step 5: Telophase - Nuclear membrane returns around each mass of chromosomes, and the cell pinches apart in the middle (“furrowing” in animal cells, or “division plate formation” in plant cells). Normal cell Step 1: Interphase Step 4: Anaphase © Mark Twain Media, Inc., Publishers Step 2: Prophase Step 5: Telophase 21 Step 3: Metaphase Cell divides, forming two daughter cells Meiosis Learning About DNA Meiosis Meiosis is cell division that produces gametes. Gametes (reproductive cells) have only half the number of chromosomes as body cells. This half-set of chromosomes is called the genome for an organism. This is important during fertilization. When reproductive cells (egg and sperm) unite, the full number of chromosomes for the formation of body cells is restored. For example, a fruit fly has eight chromosomes from both parents. It also has traits, or genetic material, from both parents. Meiosis requires two divisions of the nucleus—Meiosis I and Meiosis II. Meiosis I has steps and names like those in mitosis. During Meiosis I, the cell divides, forming two daughter cells with chromosomes still in pairs. Meiosis II begins with the two daughter cells going through a second division of the nucleus; in this process, there is no chromosome replication. The chromosome pairs are split apart, forming four daughter cells with half the number of chromosomes (single strands of chromosomes). Meiosis I Normal cell Step 4: Anaphase Step 1: Interphase Step 2: Prophase Step 5: Telophase Cell divides, forms two daughter cells Meiosis II Two daughter cells divide Forming two more cells (four total cells) © Mark Twain Media, Inc., Publishers 22 Step 3: Metaphase Learning About DNA Mitosis and Meiosis: Reinforcement Activity Name: Date: Mitosis and Meiosis: Reinforcement Activity To the student observer: Why do you think chromosomes are copied during cell division? Analyze: Is cell division a form of reproduction? Explain. Directions: Complete the following sentences. 1. is the process by which cells reproduce body cells. 2.In mitosis, the nucleus first, and then the cytoplasm. 3. During cell division, each chromosome makes an exact of itself. 4.The two new cells that are formed by mitosis are called . 5.Each body cell contains the same number of . 6. Reproductive cells are called . 7. or are produced by meiosis. 8. Gametes contain the number of chromosomes of the body cells. 9.Humans have chromosomes in their body cells, and chromosomes in their reproductive cells. 10. During mitosis, the nucleus divides divides , and during meiosis, the nucleus . Match the phase of mitosis to its proper description. 1. Chromosomes make exact copies of themselves. 2. Nucleus disappears, and fibers stretch across the cell. A. Interphase B. Prophase 3. Nuclear membranes return, and the cell pinches apart. C. Metaphase 4. Paired chromosomes line up in the middle of the cell. D. Anaphase 5. Paired chromosomes tugged to opposite ends of the cell.E. Telophase © Mark Twain Media, Inc., Publishers 23 Learning About DNA “Cell-a-bration Day”: Cell Model Project Name: Date: “Cell-a-bration Day”: Cell Model Project To the student observer: Cell-a-bration Day is a project day. It’s a day to show off your creativity, while proving you understand that the cell is three-dimensional and an important part of all organisms. You must meet the criteria and deadline your teacher sets by completing one of these projects. My Cell-a-bration Day is on . (date due) (Any project turned in late will be reduced one letter grade.) My Cell-a-bration Day Project will be a typical (check one): A. Plant Cell B. Animal Cell My project will be: (Check one) A. A three-dimensional model B. An edible cell For my project I will be: A. Working alone B. Working with a partner (partner’s name) * Exchange phone numbers so you can get together to work on your projects. Project Guidelines: Cell models should be created so that the cell parts can be seen and labeled. (You may need to include a key for your model.) It must include the name and function of the cell organelles. The cell must be large enough so everyone can see and distinguish each of the organelles. The cell model must be built or constructed by you in some way. Use any of the suggested materials discussed in class (Styrofoam™, modeling clay, salt-dough, wood, shoeboxes, and jars are all good materials to work from. Be creative and choose good representations for your cell organelles. Have a great time building your cell!). Edible cells should be made from something that is edible. This will be a food day, so plan to make enough to share with the class. All other rules apply. It must be three-dimensional with realistic representations of each of the organelles (Candies or frosting make good choices to use for the organelles. Good bases for the cytoplasm may be cookie dough, cake batter, bread or pizza dough, gelatin, or anything else that appeals to you.). © Mark Twain Media, Inc., Publishers 24 Learning About DNA You Are What You Inherit You Are What You Inherit Traits The characteristics of a living thing are called traits. What if you were asked to list ten characteristics or traits that would describe your appearance? Your list might include things like dark curly hair, brown eyes, freckles, and a height of 4′6″ tall. It would be unlikely that your list would be exactly the same as one of your classmates. This is because each person is a unique individual. All living things are grouped according to their traits. They may share many group or common traits with other members of the same group but have different individual traits. Traits that are passed on from parents to their offspring are called inherited traits. The passing on of traits from parents to offspring is called heredity. The study of heredity is called genetics. Let’s explore traits further by taking a closer look at group traits and individual or inherited traits. Group Traits It’s easy to distinguish a bird from a mammal. Feathers are a group trait among birds, while hair is a group trait among mammals. All members of a group have certain traits in common. An owl has many group traits it shares with all birds; yet, it has other traits that enable you to distinguish the owl from all of its other feathered friends. A giraffe is easy to recognize from all other mammals. Giraffes have hair, are warm-blooded, nurse their young, and give birth to live offspring like all mammals. You share many of the same group traits with the giraffe, and you share many group traits with other humans. Although humans and giraffes share many common traits, they also have different traits that enable you to distinguish one from the other. All humans share certain group traits, but no two people are exactly alike—not even identical twins. There are always individual differences called inherited traits that allow us to identify members of the same group. Individual Traits There are always individual differences called individual traits. No two organisms are exactly alike. Individual traits help us to identify members of the same group. Think of your family and friends—you can tell one from the other, can’t you? Can you think of some inherited family traits you and your family share? You are able to tell the difference between your family members by their differences or the traits they do not share in common. Some individual traits include type and coloring of skin and hair, shape of face and facial features, size, eye color, etc. © Mark Twain Media, Inc., Publishers 25 Learning About DNA You Are What You Inherit: Reinforcement Activity Name: Date: You Are What You Inherit: Reinforcement Activity To the student observer: Can you identify five traits that belong to all humans? Analyze: Can you identify these two humans by their individual traits? Write the correct boy’s name under each picture. Tom is short and very thin. He has light skin and dark curly hair. John is tall and very muscular. He has light-colored skin and dark straight hair. a. b. Part A. Directions: Study each group trait and decide if it is a mammal trait or a bird trait. 1.Hair covering is a trait. 2.Feather covering is a trait. 3.Hatching from an egg is a trait. 4. Giving live birth is a trait. 5. Nursing its young is a trait. 6.Having sharp talons and curved beaks is a trait. 7.Having light, hollow bones is a trait. 8.Having sharp canine teeth is a trait. Part B. Directions: Complete the following sentences. 1. Characteristics of living things are called . 2. Differences of individuals of the same group are called . 3. Scientists living things according to their traits. 4. Color of feathers is a(n) trait among birds. 5.Having hair is a(n) © Mark Twain Media, Inc., Publishers trait among mammals. 26 Learning About DNA What Are Dominant and Recessive Traits? What Are Dominant and Recessive Traits? Patterns of Inheritance What traits have you inherited? Every living thing is a collection of traits that have been passed down to them by their parents. These traits are controlled by something called genes. Genes are made up of DNA and are located on the chromosomes. When pairs of chromosomes separate into sex cells during a process called meiosis, pairs of genes also separate from one another. As a result, each sex cell winds up with one form of a gene for each trait the organism shows. If the trait is for hairlines, then the gene in one sex cell may control one form of the trait, such as common baldness—an “m-shaped” hairline. The gene for hairlines in the other sex cell may control another form of the trait, such as a straight hairline. The different forms a gene may have for a trait are called alleles (uh LEELZ). An allele is one pair of genes that can appear as alternatives in heredity, and they are located on equivalent portions of chromosomes. Most cells in our bodies have two alleles for every trait. Two Genes for the Trait Determine Inheritance Gregor Mendel, the father of genetics who studied the inherited traits of pea plants, noticed that genes (hereditary factors) always came in pairs. Every organism that reproduces sexually receives two genes for each trait; they receive one gene from each parent. Mendel noticed, however, that the genes were not always equal. He wondered why some traits found in the parents showed up in their offspring, while other traits did not. To find the answer, he experimented with pea plants. These experiments led to the principal of genetics called the Law of Dominance. The Law of Dominance states: • An organism receives two genes for each trait, one from each parent. • One of the genes may be stronger; the trait of the stronger gene shows up and is called the dominant gene. The trait of the weaker gene is “hidden” or does not show up and is called the recessive gene. The trait that was always visible in the offspring was considered to be the stronger of the two. If the trait always showed up in the offspring, he called that gene the dominant gene for that particular trait. The other gene, weaker and usually hidden by the stronger gene, was called the recessive gene for that trait. If an offspring receives two of the same genes (either two dominant genes or two recessive genes), the offspring will inherit or have that trait. There are no other possibilities. An organism with two alleles for a trait that are exactly the same is called homozygous (HO muh ZI gus). An organism with two different alleles for a trait is called heterozygous (HET uh roh ZI gus). Pure Traits Pure traits can be either recessive or dominant. Pure traits may have two dominant genes or two recessive genes. For example, a pea plant may have two genes for tallness, which is a dominant trait in pea plants. This plant is a homozygous plant with a pure dominant trait for tallness. All of the offspring from this plant will be tall. A pea plant with two genes for shortness is also a pure organism. However, shortness in pea plants is a recessive trait. This plant is a © Mark Twain Media, Inc., Publishers 27 Learning About DNA What Are Dominant and Recessive Traits? What Are Dominant and Recessive Traits? (cont.) homozygous plant with a pure recessive trait for height. The offspring from this plant will be short if it pollinates with another plant that has two genes for shortness. If this plant pollinates with a tall pea plant, the tall dominant gene will mask or cover up the recessive gene for shortness. Both plants are homozygous or pure plants; one is a pure dominant pea plant, the other is a pure recessive pea plant. Hybrid Traits Organisms that have two unlike genes for a certain trait are called hybrid. A pea plant with one recessive gene for shortness and one dominant gene for tallness is a hybrid for that trait. A hybrid is called heterozygous, as it has two different alleles. The offspring from a pure tall pea plant, cross-pollinated with a pure short pea plant, will result in a heterozygous plant for tallness. No organism has all dominant or all recessive genes. An organism may be pure in certain traits and hybrid in others. Remember, student observers, that a dominant trait in one kind of organism may be a recessive trait in another organism. Homozygous Traits Dominant Trait Recessive Trait pure tall pure Short T T t t Gene from female Gene from male Gene from female Gene from male Heterozygous Traits Hybrid Trait hybrid tall T t Gene from female Gene from male © Mark Twain Media, Inc., Publishers 28 Learning About DNA What Are Dominant and Recessive Traits?: Reinforcement Activity Name: Date: What Are Dominant and Recessive Traits?: Reinforcement Activity To the student observer: Based on what you have learned, can you explain why Zach’s hair is dark like his mother’s and not blond like his father’s? Analyze: What is the difference between a pure tall plant and a hybrid tall plant? Directions: Complete the following sentences. 1.The gene that always shows itself is called the 2. All short pea plants have two gene. genes. 3. An organism with two like genes for a trait is called for that trait. 4.Each trait an organism has is determined by one gene from parent. 5. Most cells in our bodies have alleles for every trait. 6.The “hidden” gene that does not show up is the gene. 7. An organism with two alleles that are exactly the same for a certain trait is called . 8. An organism with two different alleles for a trait is called © Mark Twain Media, Inc., Publishers 29 . Learning About DNA Dominant and Recessive Traits in Humans: Reinforcement Activity Name: Date: Dominant and Recessive Traits in Humans: Reinforcement Activity Human genetics is very difficult to study, because the life span of humans is so long compared to the life span of other animals and plants. As a result, scientists cannot study all of the offspring produced in many generations of one family. Another difficulty in the study of human genetics is the number of offspring. Humans produce fewer offspring than other animals and plants. It is difficult to compare traits with fewer offspring to observe. Scientists use what they learn from studying other animals and plants to learn more about human genetics. How many of the traits in the table below do you recognize in yourself? Dominant Brown eyes Curly hair Freckles Nearsighted eyes Long eyelashes Detached earlobes Dimples Widow’s peak hairline Recessive Blue eyes Straight hair No freckles Normal eyes Short eyelashes Attached earlobes No dimples Straight hairline Predicting Human Traits To the student observer: Use the information in the table above to see if you can predict offspring traits in the chart below. The first example has been done for you. Mother Father Offspring 1. normal eyesight nearsighted 2. straight hair straight hair 3. freckles freckles 4. long lashes short lashes 5. no dimples dimples 6. detached lobes detached lobes 7. blue eyes brown eyes 8. widow’s peak nearsighted Dominant/ Recessive Hybrid/ Pure dominant hybrid straight hairline Analyze: How many offspring will be pure dominant for a trait? Why do recessive genes show up? Answer on your own paper. © Mark Twain Media, Inc., Publishers 30 Learning About DNA FYI: Mendelian Traits FYI: Mendelian Traits Your genes, units in the chromosomes that contain your dominant and recessive traits, have been inherited from your parents and grandparents. Below is a fun list of some common Mendelian traits. Do you have any of these traits? Tongue Rolling - dominant - ability to roll tongue into a longitudinal u-shaped tube Tongue Folding - recessive - to fold the tip of your tongue back upon the main body of the tongue without using your teeth Detached Earlobes - dominant - earlobes not directly attached to your head; free-hanging Attached Earlobes - recessive - earlobes directly attached to the head Darwin’s Tubercle - dominant - little bump of cartilage on outer rim of ear Hitchhiker’s Thumb - dominant - thumb, when up in the hitchhiking position, can bend backwards at a sharp angle (50% or more) Relative finger length - dominant - index finger longer than ring finger Dimples - dominant - natural smile produces dimples in one or both cheeks or a dimple in the center of the chin Widow’s peak - dominant - pull hair off your forehead; hairline comes to a point in the middle of forehead Bent little finger - dominant - little finger curves in toward other fingers Webbing - recessive - Spread fingers apart and grasp a good thumbful of skin. Blaze - dominant - lock of hair noticeably different color; won’t take dye Freckles - dominant - circular pattern of skin coloration Whorl - can be dominant or recessive - Which way does the hair at the crown of your head turn? Have a partner stand behind you to check which way your hair turns: if it spirals clockwise, the whorl is dominant; if it spirals counterclockwise, the whorl is recessive © Mark Twain Media, Inc., Publishers 31 Learning About DNA Predicting Heredity Predicting Heredity Gene Symbols All organisms have at least two genes for every trait. They receive at least one from each parent. Symbols are used to help in predicting the traits of offspring. A capital letter is used to represent a dominant trait. A lowercase letter is used to represent a recessive trait. In humans, brown eyes are dominant. The symbol for this gene is B. The gene for blue eyes is recessive. The symbol for this gene is b. A capital letter shows that the gene for that trait is dominant. A lowercase letter shows that the gene for that trait is recessive. If black fur color in guinea pigs was a dominant trait, what symbol would be used for that gene? If you’re thinking that it is a capital B, you’re right. A guinea pig with white fur is a recessive trait, so the symbol for that gene is represented with a lowercase b. Punnett Squares One way to predict heredity is to use a special chart called a Punnett square. A Punnett square shows the possible gene combinations for a trait and consists of four boxes inside a square. Each square represents a possible gene combination. The parents’ genes are placed outside the square. The steps below will show you how to predict the possible gene combinations from two parents. • Draw a box with four squares. • Write the genes from the mother down the left side of the square. • Write the genes from the father across the top of the square. •Fill in each of the four boxes by giving one gene from each parent to each box—one gene from the mother and one gene from the father. Example of a Punnett square: B b B BB Bb b Bb bb Incomplete Dominance In most sports, there is usually a stronger team and a weaker team. Which team usually wins? What happens if the two teams are equally matched? Heredity can work like that too. If the gene is dominant, it usually wins over the weaker recessive gene. Some genes of certain traits are equally strong. We call this incomplete dominance. In these traits, a mixture of both traits shows up in the offspring. This kind of gene combination is called blending. In some flowers, the color red (RR ) is equally as strong in heredity as the color white (WW ). If neither color is dominant, the offspring will be a combination or blending of the two colors red and white. If neither color is dominant, what color will the offspring be? If you are thinking red and white make pink, then you’re absolutely right. Since neither color can hide the other color, a blending of the two occurs. A Punnett square for the cross-pollination of these two flowers is demonstrated on the next page. © Mark Twain Media, Inc., Publishers 32 Learning About DNA Predicting Heredity Predicting Heredity (cont.) R R W RW RW W RW RW The offspring of crossed pure red and pure white flowers are a blending of the two colors. How can you tell, observers, from looking at the chart above, that there is incomplete dominance? If you’re thinking because two capital letters are used to symbolize their gene combinations, you’re correct. Incomplete dominance produces offspring with hybrid genes for the given trait, and neither one is dominant over the other for that trait. Examples in humans of incomplete dominance are found in skin, hair, and eye color. Let’s hear it for the green-eyed people! Genotypes and Phenotypes The genetic makeup of an organism is its genotype. The genotype of the pink flowers is RW. The genotype of the red flower is RR, and the white flower’s genotype is WW. The capital letters indicate incomplete dominance. The genotype is the combination of genes for each trait the organism has. The physical trait that shows as a result of the genotype is the phenotype. The phenotype for RW is the color pink. Remember, you can not always figure out the genotype by looking at the phenotype. The gene combination TT and Tt both produce tall pea plants, giving them the same phenotype or physical characteristic. The capital T that indicates tallness in pea plants is a dominant trait. TT is pure dominant and T is dominant over t in the hybrid tall pea plant. Both plants are tall pea plants, but each has a different genotype. Explore the examples below to gain a better understanding of the terms genotype and phenotype. Trait Genotype Phenotype 1. Red flower RR Red Color 2. White flower WW White Color 3. Pink flower RW Pink Color 4. Brown eyes BB Brown Color 5. Blue eyes bb Blue Color 6. Brown eyes Bb Brown Color 7. Tall plant TTTallness 8. Short plant tt Shortness 9. Tall plant TtTallness © Mark Twain Media, Inc., Publishers 33 Learning About DNA Predicting Heredity: Reinforcement Activity Name: Date: Predicting Heredity: Reinforcement Activity To the student observer: Meet George and Gina Guinea Pig. They are expecting offspring very soon. See if you can use a Punnett square to predict the possible gene combinations of their offspring. George has two of the same genes for fur color. He is pure dominant for black fur. Gina has two of the same genes for white fur. She is pure recessive for white fur. George has the genotype BB, and Gina has the genotype bb for the trait. Use the Punnett square below, and determine possible gene combinations for their offspring. Analyze: 1. How many gene combinations are there? 2. What is the genotype of their offspring? 3. What color will the offspring be? Why? To the student observer: Meet Mr. and Mrs. Jones. Gary Jones has dark hair. He has two of the same genes for hair color. He is pure for dark hair coloring. His genotype is DD for hair color. Tina Jones has dark hair too. She has two different gene combinations. She has one dominant gene for dark hair and one recessive gene for blonde hair. She is a hybrid with the genotype Dd. Based on your knowledge of Punnett squares, what hair color will their children have? Analyze: 1. What are the two genotype possibilities for hair color? 2. What percent or fraction of their children will be pure for dark hair? 3. What hair color will their children have? 4. If Gary and Tina were both hybrid darks for hair coloring, could they have a child with blonde hair? Fill in the correct fractions below. The first one has been done for you.  would be pure dominant for hair color would be pure recessive for hair color would be hybrid © Mark Twain Media, Inc., Publishers 34 Learning About DNA How Does DNA Work? How Does DNA Work? Structure and Function Picturing DNA as a ladder helps in understanding how the substances are arranged in the molecule. However, the two DNA strands (sides) come apart easily like a zipper. A DNA molecule is better described as a twisted zipper. DNA not only directs every cell in our bodies, but it also allows the cells to replicate (copy themselves) and pass the genetic information on to the new cells. The function of DNA is to use itself as a pattern to copy an organism’s genetic information. DNA determines how an organism looks and acts. Every cell inside the organism has the same genetic code or blueprint that is unique only to that organism. DNA is responsible for passing on the code from one generation to the next. During mitosis (cell division), the DNA unzips and gives each new cell a copy of itself. Genes are sections of DNA that code for a definite function. The DNA codes use four symbols (A, T, C, G) for each of the four bases. The sequencing (arrangement) of the bases determines the function of DNA. The four base compounds will only pair with one of the other base compounds. If you know the base sequence on one side, it is easy to duplicate the entire molecule. If you know the base pair rules and you know the sequence of the first strand, you can predict the second strand of DNA. For example, if the first strand is AAGGCG, then the other strand is TTCCGC. Remember, wherever there is an A in one strand, there will be a T in the other. Wherever there is a G in the first strand, there will be a C in the opposite strand. When the chromosomes are doubled at the beginning of mitosis, the amount of DNA is also doubled. The process of how DNA copies itself is pictured below by using the Watson and Crick model. How DNA Copies Itself Step 1. An enzyme breaks the bonds between the nitrogen bases. (strands separate) Step 2. The bases attach to each strand, then pair up with the correct bases from a supply found in the cytoplasm. The order of the new base pairs will match the order of the original DNA before it separated. Step 3. Sugar and phosphates form the sides of each new DNA strand. Each molecule now contains an original strand of DNA and a new strand. DNA and Protein Synthesis All cells have cytoplasm—the part of the cell outside the nucleus. The information in DNA forms proteins inside the cytoplasm. All living things need proteins. Proteins are made up of units called amino acids that are linked together in a certain order. A protein may be made up of hundreds of thousands of amino acids. The order of the amino acids determines the kind of protein. Some proteins form cell structures, while other proteins called enzymes regulate everything that goes on inside the cell. Enzymes do their work in special structures inside the © Mark Twain Media, Inc., Publishers 35 Learning About DNA How Does DNA Work? How Does DNA Work? (cont.) cell cytoplasm. The enzymes in the mitochondria specialize in energy production. The section of DNA on a chromosome that directs the making of a protein is called a gene. If production of proteins takes place in the cytoplasm, does DNA leave the nucleus? No, DNA molecules are too large to pass through the pores of the nuclear membrane. The code must be carried by a second type of nucleic acid, called ribonucleic acid or RNA. RNA is different from DNA. It is a shorter, single strand; therefore, it can pass through the pores of the nuclear membrane. Since it carries the genetic information as a kind of message, it is called messenger RNA or mRNA. RNA is a different form of DNA; it has a different sugar known as ribose (R), and instead of thymine, it has a different nitrogen base, uracil (U). RNA is made in the nucleus on a DNA pattern. RNA is formed when strands in a section of DNA unwind and open up. The bases, sugars, and phosphates inside the nucleus join with part of the DNA to form RNA. After RNA has been formed, it separates from DNA. RNA then moves out into the cytoplasm, carrying the information in its base sequence. After enough RNA copies are made, the two strands of DNA close back together. There are two types of RNA: messenger RNA (mRNA) and transfer RNA (tRNA). Protein assembly begins with the mRNA molecule moving out of the nucleus and attaching to ribosomes. Pieces of tRNA pick up and carry specific amino acids in the cytoplasm to the ribosomes and temporarily pair up with the appropriate triplet code on the mRNA molecule. When the amino acids are in place, they bond together, and the message has now been translated into a specific protein molecule. Mutations Sometimes changes in the code occur during replication, and the traits of an organism are changed. If an error is made in the genetic code, the permanent change is called a mutation. The change may or may not be life-threatening. Some mutations add variety to a species. Outside factors, such as X-rays and chemicals, have been known to break (change) chromosomes. If a mutation occurs in the reproductive cells, the mutation will be passed on to the offspring. Uses of DNA DNA has become very valuable to law enforcement officials in helping officers solve crimes by identifying criminals. It can also be used in a court of law to prove innocence or family relationships. DNA is used in genetic engineering (a method to make new forms of DNA) to improve living things. It is used to treat defective genes associated with inherited diseases, such as sickle-cell anemia, Tay-Sachs disease, or hemophilia. Agriculture uses DNA to improve crops and livestock. Animal breeders use DNA to produce livestock offspring with desirable traits. Mankind has developed genetically engineered medicines, such as insulin for diabetics, that help many people live better lives. However, care must be taken not to accidentally produce a harmful organism for which there is no cure. © Mark Twain Media, Inc., Publishers 36 Learning About DNA How Does DNA Work?: Reinforcement Activity Name: Date: How Does DNA Work?: Reinforcement Activity To the student observer: Can you describe the appearance and function of DNA? Analyze: What might occur if there was an extra nitrogen base in the middle of the mRNA code? Part A. Directions: Complete the following sentences. 1. DNA copies itself when the two strands and replicate identical strands. 2. Proteins are made up of units called . 3. DNA strands are held together by and separated by when DNA copies itself. 4. are sections of DNA that code the making of a specific protein. 5. All need proteins to build cells and tissue. 6. are special proteins that control activities going on inside the cell. 7. carries the code for proteins from the nucleus to the ribosomes. 8. picks up amino acids in the cytoplasm and moves them to the ribosomes. Part B. Directions: Answer the following questions. 1.How is RNA different from DNA? 2. List three uses for DNA. © Mark Twain Media, Inc., Publishers 37 Learning About DNA Modeling the Structure of DNA: Reinforcement Activity Name: Date: Modeling the Structure of DNA: Reinforcement Activity Analyze: Before you begin to construct the model, remember what you’ve learned about the DNA molecule. Activity 1 Materials: Pair of scissorsTracing paper Construction paper (white, black, blue, green, red, yellow) Procedure: 1.Using tracing paper, trace the DNA parts shown here. 2.Trace and cut out 12 black sugar molecules and 14 white phosphate molecules. Be sure to label the molecules. 3. Now you are ready to trace 3 blue T’s, 3 green A’s, 3 red G’s, and 3 yellow C’s. 4. Construct the sides (backbone) of the molecule with the sugars and the phosphates. 5.It’s time to complete the DNA molecule by fitting the base pairs correctly along the sides of the molecule. Activity 2 Materials: Use materials such as modeling clay, Styrofoam™ balls, or gumdrops with toothpicks or straws to build a model of the DNA molecule. Each color, size, and kind of ball should represent each molecule that makes up DNA (the four bases and the two chemicals that make up the backbone). The straws and toothpicks will represent the bonds between the molecules. Be sure to include a key for your molecules. Questions and Conclusions: 1. Which nitrogen base pairs with G? With A? 2. Which chemicals make up the backbone of the double helix? 3. Which chemicals make up the rungs (steps) of the double helix? 4. Do you think your model looks exactly like your classmates’? Explain. © Mark Twain Media, Inc., Publishers 38 Learning About DNA Some DNA to Study: DNA Research Project Some DNA to Study: DNA Research Project Scientists have found many ways to improve our lives and the lives of plants and animals by making use of new technology in the field of genetics. If Gregor Mendel were alive today, he would certainly be amazed to see how far researchers have taken his early studies of genetics. To the student observer: You have been learning the basics of DNA. Can you apply what you’ve learned to create a fantastic classroom project? Let’s create a classroom DNA scrapbook. You and a partner will take off on a journey to the resource area and computer lab to discover why genetics is important. It will take the entire class to just scratch the surface of this amazing field of science. Hardly a day goes by that there isn’t a newspaper article about the latest information on genetic research. The word “gene” has become a household word. Choose a genetic research topic to include in your scrapbook. Below is a list of suggested topics; however, you may also select a topic of your own. Bright Ideas Inherited/Sex-linked Disorders Tay-Sachs disease Down’s Syndrome Cystic Fibrosis Sickle cell anemia Hemophilia Colorblindness Genetic Engineering Recombinant DNA Gene Therapy Cloning New Medicines Crime Investigation Controlled Breeding Mutation Human Genome Project Class Scrapbook: Keep the class reports about DNA topics in a special book. Organize the reports into the scrapbook by related topics. How to make: 1. Make the cover from heavy cardboard. The cover should be slightly larger than the pages in the book. Have interested students submit cover designs. Let students vote on the design they prefer. The student with the winning idea should make the cover for the scrapbook. 2. Punch holes in 30 sheets of construction paper and the cover. Lace it all together with a shoelace, or bind it with metal rings. This will allow you to add or remove pages. Display the finished project for your students and visitors to see. Students may want to bring in related articles to accompany their reports. These may be included in the scrapbook as well. © Mark Twain Media, Inc., Publishers 39 Learning About DNA DNA Vocabulary: Study Sheet Name: Date: DNA Vocabulary: Study Sheet To the student observer: Below is a list of important terms for the DNA unit. Use this list of terms and their definitions to help you complete the activities on the following pages. This study sheet will also help you prepare for the unit test. 1. Adenine - a white, crystalline purine base contained in DNA; links with thymine 2. Base pair - two of four nitrogen bases linked together in each double strand of DNA 3. Cell - the smallest unit of life; combines to form tissue in plants and animals 4. Chromosomes - rod-shaped bodies inside the cell’s nucleus; carry the genetic code 5. Covalent bond - the chemical bond formed between the nitrogen bases and the sugarphosphate backbone in DNA 6. Cytosine - a pyrimidine base contained in DNA; links with guanine 7. Daughter cells - the two new cells formed during mitosis 8. Deoxyribonucleic Acid (DNA) - the hereditary material that makes up chromosomes and genes; an extremely long double helix (spiral) molecule that contains four nitrogen bases and a sugar and phosphate backbone 9. Dominant gene - the stronger gene for a trait; always shows up in the offspring 10. Genes - made up of DNA; located on the chromosomes 11. Genetics - the study of traits in an organism and how they are passed on from the parent to the offspring 12. Genetic code - the order in the DNA molecule of the four nitrogen bases 13. Guanine - a crystalline purine base contained in DNA; links with cytosine 14. Hybrid - having two unlike genes or alleles; such as Tt or WR 15. Meiosis - a process that requires two divisions of the nucleus to form gametes (reproductive cells) 16. Mitosis - a process in which cells divide to form new body cells 17. Non-covalent bonds - a weak electrical attraction between the partially negative atoms on the base of one side with the partially positive atoms on the other 18. Punnett square - a chart used to predict hereditary traits in offspring 19. Recessive gene - the weaker, “hidden” gene for a trait 20. Thymine - a white, crystalline, pyrimidine base contained in DNA; links with adenine © Mark Twain Media, Inc., Publishers 40 Learning About DNA DNA Crossword Puzzle Name: Date: DNA Crossword Puzzle Directions: Use the clues below and other resources to complete the crossword puzzle. 1 4 2 3 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Across 2.The information carried in the chromosomes of an organism 6.The nitrogen base that pairs with thymine 7. Smallest membrane-bound unit of life; forms tissue in plants and animals 11. A process in which cells divide to form new body cells 13. Made up of DNA and are located on the chromosomes inside the cell’s nucleus 17. : a molecule that consists of two complementary strands connected by base pairs 18.Having two like genes or alleles, such as TT or tt 19. A chart used to predict hereditary traits in offspring (two words) Down 1. Partner of Watson; helped make the first model of the DNA molecule (last name) 2.Experimented with pea plants to learn about inherited traits; Father of Genetics (two words) © Mark Twain Media, Inc., Publishers 41 3.The spherical membrane-bound structure in a cell that contains the DNA 4.The sugar-phosphate supporting structure of the DNA double helix is called the . 5.The passing of traits (and genes) from one generation to the next 8.The order of the four nitrogen bases in the DNA molecule (two words) 9.The nitrogen base that pairs with guanine 10.Two of four nitrogen bases linked together in each double strand of DNA (two words) 12.The stronger gene for a trait; always shows up in the offspring (two words) 14. Spooled strings of genes inside the nucleus; rodshaped and carry the genetic code 15.Having two unlike genes or alleles; such as Tt or RW 16.The two new cells formed during mitosis: Learning About DNA DNA Unit Test Name: Date: DNA Unit Test Part A. Directions: Put the letter of the correct answer on the blank. 1. A Punnett square shows possible combinations of a. DNA b. chromosomes c. genes d. traits 2. The sides or backbone of the DNA ladder are made up of a. nitrogen bases b. proteins c. sugars and phosphates d. adenine 3. A pea plant with two tall genes is said to be a. pure tall b. hybrid tall c. blended d. hybrid short 4. Characteristics that an organism has are its a. traits b. genes c. DNA d. chromosomes 5. An organism with two like genes for a trait is said to be a. hybrid b. pure c. dominant d. recessive 6. A molecule of DNA contains all of the following except a. nitrogen bases b. sulfur c. sugar d. phosphates 7. When one parent is pure dominant and the other parent is pure recessive, the offspring will all be a. hybrid recessive b. pure recessive c. pure dominant d. hybrid dominant 8. A gene that always shows up in the offspring is a a. dominant gene b. recessive gene c. pure gene d. hybrid gene 9. The passing of traits from parents to offspring is called a. heredity b. genetics c. reproduction d. chromosomes c. chromosomes d. genes 10. Inherited traits are controlled by a. cells b. mitosis 11. A complex molecule found inside a cell and called the “thread of life” is a. DNA b. genes c. chromosomes d. heredity 12. Adenine always pairs up in the double helix with a. cytosine b. thymine c. guanine d. phosphate 13. The rungs of the ladder are pairs of a. nitrogen bases b. genetic bases c. sugar bases d. inherited traits 14. A microscope containing two or more lenses is a a. compound b. electron c. simple microscope. d. stereoscope 15. A microscope that uses electrons to magnify a living cell is a a. TEM © Mark Twain Media, Inc., Publishers b. SEM c. electron microscope 42 d. stereoscope Learning About DNA DNA Unit Test Name: Date: DNA Unit Test (cont.) Part B. Directions: Match the following microscope functions with its corresponding part. 16. Used to hold slides in place a. Objectives 17. Holds objectives and rotates for magnification b. Nosepiece 18. Supports the body tube c. Diaphragm 19. Supports the object for viewing d. Stage 20. High and low power lenses e. Arm 21. Regulates the amount of light that f. Stage clips enters the body tube Part C. Directions: Match each of the following descriptions with its corresponding term. 22. The building blocks of life a. Eukaryotic 23. A cell without a true nucleus b. Prokaryotic 24. Living material inside the cell, c. Cells except the nucleus 25. Controls all cell activities d. Mitochondria 26. Animals and plants have this kind of cell e. Gametes 27. The powerhouse of the cell f. Nucleus 28. Transportation network of the cell g. ER 29. Process in which cells divide h. Cytoplasm 30. Cell division that produces gametes i. Meiosis 31. Humans have 46 of these in their body cells j. Daughter cells 32. New cells formed by mitosis k. Mitosis 33. Cells that have half the number of chromosomes l. Chromosome Part D. Directions: Match each of the following descriptions with its corresponding DNA term. 34. Found on the chromosomes; come in pairs a. Base pair 35. During cell division, DNA is . b. Chromosomes 36. Changes that occur during replication are . c. Genes 37. Order in the DNA molecule forms the . d. Genetic code 38. The study of traits and how they are passed on e. Replicated/Copied 39. Rod-shaped, spooled string of genes f. Mutations 40. Two of four nitrogen bases linked together g. Genetics in each double strand of DNA © Mark Twain Media, Inc., Publishers 43 Learning About DNA Answer Keys Answer Keys What is DNA?: Reinforcement Activity (p. 3) To the student observer: The differences in the information stored in the form of DNA (genetic code). Analyze: Identical or the same. 1. A large complex organic molecule found inside the cell’s nucleus on structures called chromosomes. 2. A twisted miniature ladder or a spiral staircase. 3. Phosphate, sugar or deoxyribose, and four nitrogen bases. 4. Phosphate and sugar 5. Pairs of nitrogen bases 6. Adenine pairs only with thymine; cytosine pairs only with guanine. Learning About Microscopes: Reinforcement Activity (p. 8) To the student observer: By the arm and the base Analyze: You see greater details and less of the object when using high power 1.The number of lenses 2.On the stage 3.Hans and Zacharias Janssen 4. 500X 5.The adjustment knobs; use the coarse adjustment first. 6.To look at objects too small to be seen with a compound light microscope; to see cell structures 7. When you wanted to see a three-dimensional view How to Use a Microscope: Reinforcement Activity (p. 11) 1.The letter e appears to be reversed or backwards. 2.Opposite; if moved forward, it appears to move backward. 3. Nylon thread is thinner and very tightly woven. Wool is thicker and loosely woven. 4. Wet-mount: place the object for viewing on a slide, and then add a drop of water; cover with a cover slip 5. So you don’t scratch or break the slide. 6. Coarse adjustment 7.High: answers will vary. Low: usually 5X or 10X 8.Objective lens multiplied by the eyepiece lens; eyepiece times the objective lens. Example: 10X x 40X = 400X (10 x 40 = 400) The Cell: Reinforcement Activity (p. 13) To the student observer: Because DNA is located in the cell structure called the nucleus. Analyze: As microscopes improved, scientists were able to see and study the parts of the cell better. 1. Cells 2. Robert Hooke 3. dead plant © Mark Twain Media, Inc., Publishers 4. Anton van Leeuwenhoek; living 5. Cell Theory 6. Schleiden, Schwann, Verchow 7.Histologists 8. a.All organisms are made up of one or many cells. b. Cells are the basic unit of structure and function in an organism. c. All cells come from other cells that already exist. Cell Organization: Reinforcement Activity 1 (p. 15) To the student observer: It protects and encloses the nucleus and controls movement of materials into and out of the nucleus. Analyze: The cell would die because it wouldn’t run properly. 1.The nucleus 2. a. Shapes the cell b. Protects the cell c. Controls the movement of materials into and out of the cell. 3. a. Prokaryotic cells - without a membrane-bound nucleus b. Eukaryotic cells - have a true or membrane-bound nucleus 4.The cytoplasm 5. A. Nucleus B. Cell membrane C. Cytoplasm Cell Organization: Reinforcement Activity 2 (p. 17) To the student observer: Organelles are cell parts that have a special job to do. Analyze: Cells need energy to perform life’s functions. Muscle cells would contain more mitochondria. 1.They are filled with organelles that work like machines, each performing a certain job. It takes all of them to run the cell. 2. a. encloses the cell b. controls movement into and out of the cell c. offers shape and protection for the cell 3. a. associated plant cells b. associated animal cells, c. free-living plant cells d. free-living animal cells 4. A. mitochondria B. nucleus C. chloroplast D. cell membrane E. cell wallF. cytoplasm G. Golgi bodies H. endoplasmic reticulum I. vacuole J. ribosomes I’m Made of These?: Student Lab (p. 19) A.vacuole B. cell wall C. cell membrane D. cytoplasm E. nucleus F. chloroplasts 44 Learning About DNA Answer Keys Prove You Can: Reinforcement Activity (p. 20) Part A: To the student observer: 1. onion, elodea 2. onion, elodea 3. onion, elodea, cheek 4. cheek 5. onion, elodea 6. onion, elodea, cheek 7. cheek 8. cheek 9. onion, elodea 10. onion, elodea, cheek Part B: Analyze 1. d 2. a 3. e 4. c 5. b Part C: Predict Cells, rectangular in shape Dominant and Recessive Traits in Humans: Reinforcement Activity (p. 30) To the student observer 2. straight hair; recessive; pure 3. freckles; dominant; pure 4. long lashes; dominant; hybrid 5. dimples; dominant; hybrid 6. detached lobes; dominant; pure 7. brown eyes; dominant; hybrid 8. widow’s peak; dominant; hybrid Analyze: 2 offspring; if the offspring receives two of the same gene, then they inherit that trait. Mitosis and Meiosis: Reinforcement Activity (p. 23) To the student observer: To make sure each new cell has the correct number of chromosomes and genetic information. Analyze: Yes, a new cell is made just like the parent cell (asexual reproduction). Part A 1. Mitosis 2. divides 3. copy 4. daughter cells 5. chromosomes 6. gametes 7. reproductive cells or gametes 8. half 9. 46, 23 10. once, twice Part B 1. A 2. B 3. E 4. C 5. D You Are What You Inherit: Reinforcement Activity (p. 26) To the student observer: vertebrate, mammal, warmblooded, have hair, give birth to live offspring, nurse their young Analyze: a. Tom b. John 1. mammal 2. bird 3. bird 4. mammal 5. mammal 6. bird 7. bird 8. mammal Part B 1. traits 2. individual traits 3. group 4. individual 5. group What Are Dominant and Recessive Traits?: Reinforcement Activity (p. 29) To the student observer: Blond hair coloring in humans must be a recessive trait, or the dominant dark hair gene hides the recessive blond hair gene. Analyze: Pure tall has two tall genes; hybrid tall has one tall gene and one short gene. 1. dominant 2. short 3. pure 4. each 5. two 6. recessive 7. homozygous 8. heterozygous © Mark Twain Media, Inc., Publishers Predicting Heredity: Reinforcement Activity (p. 34) To the student observer: B B b Bb Bb b Bb Bb Analyze 1. 1 2. Bb 3. black; hybrid - dominant gene will show up To the student observer: D D D DD DD d Dd Dd Analyze: 1. DD and Dd 2. 50% or 1/2 3. dark 4. yes 5. 1/4, 1/4, 1/2 How Does DNA Work?: Reinforcement Activity (p. 37) To the student observer: It’s a double spiral like a twisted ladder or zipper. The two sides are connected by 4 bases. It copies genetic material and passes the code to the new cells. Analyze: A mutation would probably occur. Part A 1. separate 2. amino acids 3. nitrogen bases; proteins or enzymes 4. genes 5. organisms or living things 6. enzymes 7. mRNA 8. tRNA 45 Learning About DNA Answer Keys/Bibliography Part B 1. RNA is a smaller, single-stranded molecule that has a different sugar and nitrogen base. 2. Answers will vary. Some answers might include: identifying criminals, proving family relationships, creating new medicines, treating inherited diseases, producing better crops and livestock. Modeling the Structure of DNA: Reinforcement Activity (p. 38) Activity 2 1. cytosine “C”; Thymine “T” 2. phosphates and sugar 3. Nitrogen bases 4. No, the base pairs can occur in a variety of ways. DNA Crossword Puzzle (p. 41) 1 C 4 5 B H 6 9 C 10 R 2 G E 3N O M E R U 7 C E L L 8 A D E N I N E G C R C G L E K E K O E N B D R U I S M S B Y A T S O N T E O I G E N E S E Y N M C 11 M I T O S 13 P I A N I 14 C 15 H Y 17 D E O X Y R 18 P U R E S H 16 3. a 7. d 11. a 15. a 4. a 8. a 12. b Part B 16. f 20. a 17. b 21. c 18. e 19. d Part C 22. c 26. a 30. i 23. b 27. d 31. l 24. h 28. g 32. j 25. f 29. k 33. e Part D 34. c 38. g 35. e 39. b 36. f 40. a 37. d E 12 D T D D I C A E N O I B O N U C L E DNA Unit Test (p. 42–43) Part A 1. c 2. c 5. b 6. b 9. a 10. d 13. a 14. a I C A C I D O R G N M I H T O D T G S E E O R N M C E E E S L E L 19 P U N N E T T S Q U A R E Bibliography Aaseng, Nathan. Genetics: Unlocking the Secrets of Life. The Oliver Press, Inc. 1996. Bernstein, Schachter, Winkler, Wolfe. Concepts and Challenges in Life Science. Globe 1991. Biggs, Daniel, and Ortleb. Life Science. Glencoe/McGraw-Hill, 1997. Dunbar, Robert. Heredity. Franklin Watts, 1978. Lerner, Marguerite Rush, M.D. Who do You Think You Are? The Story of Heredity. Prentice-Hall, Inc., 1963. Silverstein, Alvin and Virginia. The Genetics Explosion. Macmillan Publishing Company, 1980. Wilcox, Frank H. DNA: The Thread of Life. 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