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The Transmission of Hereditary Characteristics BLG–5065-2 Learning Guide THE TRANSMISSION OF HEREDITARY CHARACTERISTICS BLG-5065-2 Learning Guide The Secondary V biology learning guides are published by SOFAD The Human Respiratory System The Human Reproductive System and the Perinatal Period The Transmission of Hereditary Characteristics The learning guides in this collection have been adapted from the online courses of the same name which were produced first. The decision to produce both an online and a printed version of the same course was made to meet the requirements of those who do not have access to the Internet or who prefer to work with “paper,” in accordance with the need to diversify the tools and venues for distance learning. The Transmission of Hereditary Characteristics This learning guide was produced by the Société de formation à distance des commissions scolaires du Québec (SOFAD). Project coordinator: Jean-François Bojanowski (SOFAD) Pedagogical design: Jean-François Bojanowski (SOFAD) Jean-Simon Labrecque (SOFAD) Author: Jean-Marc Robitaille (Didactica) Illustrations: Sylvie Leduc Pedagogical revision: Jean-François Bojanowski (SOFAD) Diane Ménard Translation: Claudia de Fulviis Linguistic Revision: Barbara Chunn Proofreading: Valérie Champoux Claudia de Fulviis Graphics and Layout: Daniel Rémy First Edition: February 2010 January 2016 © Société de formation à distance des commissions scolaires du Québec All rights for translation and adaptation, in whole or in part, reserved for all countries. Any reproduction by mechanical or electronic means, including micro-reproduction, is forbidden without the written permission of a duly authorized representative of the Société de formation à distance des commissions scolaires du Québec (SOFAD). Legal Deposit - 2010 Bibliothèque et Archives nationales du Québec Library and Archives Canada ISBN 978-2-89493-380-0 Table of Contents of This is a preview : General Introduction .................................................................................................... VII The Biology Program ............................................................................................ troduction; and VII - the in e. Using the Learning Guide ..................................................................................... - the first modul Evaluation VII ........................................................................................................ IX Succeeding at Distance Learning .......................................................................... IX The Transmission of Hereditary Characteristics .................................................... X Reader’s Comments ............................................................................................. XI Section 1 – The Mechanisms of Heredity ...................................................................... 1.0 Module 1 – Cell Basics .......................................................................................... 1.1 ◆ The Cell ................................................................................................. 1.4 ◆ Genes .................................................................................................... 1.16 Module 2 – Cell Division ....................................................................................... 2.1 ◆ Mitosis ................................................................................................... 2.4 ◆ Meiosis .................................................................................................. 2.13 Section 2 – The Laws of Heredity .................................................................................. 3.0 Module 3 – Mendel’s Experiments ........................................................................ 3.1 ◆ Basic Concepts ....................................................................................... 3.4 ◆ Mendel’s Laws ........................................................................................ 3.17 Module 4 – Crossbreeding .................................................................................... 4.1 ◆ Monohybrid Crosses ............................................................................ 4.4 ◆ Dihybrid Crosses .................................................................................... 4.19 Section 3 – Health Problems Related to Heredity ......................................................... 5.0 Module 5 – The Heredity of Blood Types ............................................................. 5.1 ◆ The Antigens and Antibodies Specific to Blood Types ............................. 5.4 ◆ The Transmission of Alleles Responsible for Blood Types ....................... 5.19 Module 6 – Sex Chromosomes, Mutations and Hereditary Diseases ....................... 6.1 © SOFAD ◆ The Transmission of Sex-linked Genes ................................................... 6.4 ◆ Mutations and Hereditary Diseases in Humans ....................................... 6.17 V Unit Summaries ........................................................................................................... 7.1 Module 1 – The Cell ............................................................................................. 7.3 Genes ................................................................................................ 7.4 Module 2 – Mitosis .............................................................................................. 7.5 Meiosis .............................................................................................. 7.6 Module 3 – Basic Concepts .................................................................................. 7.8 Mendel’s Laws ................................................................................... 7.9 Module 4 – Monohybrid Crosses ......................................................................... 7.11 Dihybrid Crosses ............................................................................... 7.12 Module 5 – The Antigens and Antibodies Specific to Blood Types ....................... 7.13 The Transmission of Alleles Responsible for Blood Types .................. 7.15 Module 6 – The Transmission of Sex-linked Genes ............................................... 7.16 Mutations and Hereditary Diseases in Humans .................................. 7.17 General Conclusion ............................................................................................................ 8.1 Self-evaluation Activity ...................................................................................................... 9.1 Answer Key ........................................................................................................................ 10.1 Glossary ............................................................................................................................. 11.1 VI © SOFAD Introduction TABLE OF CONTENTS ANSWER KEY General Introduction ◆ The Biology Program The Société de formation à distance des commissions scolaires du Québec (SOFAD) welcomes you to the course entitled The Transmission of Hereditary Characteristics. This course is part of the Secondary V Biology Program for basic adult general education, which is composed of the following nine courses: BLG-5061-1 The Human Respiratory System BLG-5062-2 The Human Reproductive System and the Perinatal Period BLG-5063-2 The Human Digestive System BLG-5064-2 The Anatomy and Physiology of Cells BLG-5065-2 The Transmission of Hereditary Characteristics BLG-5066-1 The Human Skeletal and Muscular System BLG-5067-1 The Human Endocrine System BLG-5068-2 The Human Nervous System BLG-5069-1 Ecology Students who complete this 50-hour course can earn two Secondary V credits provided they pass a supervised examination administered by a Québec school board. There are no prerequisites for the courses in this program, and there is no equivalent program in the youth sector. The course’s general objective is as follows: “By learning concepts of anatomy and physiology, adults will gain a better understanding of the transmission of human hereditary characteristics, and the health problems associated with it.” ◆ Using the Learning Guide This learning guide is the main work tool for this course and has been designed to meet the specific needs of adult students enrolled in an individualized learning or a distance learning program. Furthermore, a webography can be viewed at the following internet address: http://cours1.sofad.qc.ca/ressources/fichiers/BLG_5065_webography.html The contents of this guide are divided into three main sections, which in turn are subdivided into modules, which are again subdivided into units. In each unit, the subject matter is presented in a number of ways (e.g. text, tables, illustrations, exercises) in order to facilitate mastery of the program objectives. In addition, at the end of each unit, just before the conclusion, you will be required to do a review activity in which all the main illustrations are shown in colour. By doing these exercises, you will be building an excellent summary of the entire course. Lastly, at the end of this guide you will find a conclusion, a self-evaluation activity and the corresponding answer key as well as an answer key for the exercises in the modules and a glossary. © SOFAD VII Introduction TABLE OF CONTENTS ANSWER KEY Learning Activities This guide includes theoretical sections as well as practical activities in the form of exercises. These exercises come with an answer key. Start by skimming through each part of this guide to familiarize yourself with the content and the main headings. Then read the theory carefully: ◆ Highlight the important points. ◆ Make notes in the margins. ◆ Look up new words in the dictionary. ◆ Study the diagrams carefully. ◆ Write down questions relating to ideas you don’t understand. Exercises The exercises come with an answer key found at the end of this guide. ◆ Do all the exercises and, at the end of each modules, quizzes. ◆ Read the instructions and questions carefully before writing your answer. ◆ Do all the exercises to the best of your ability without looking at the answer key. Reread the questions and your answers and revise your answers, if necessary. Then, check your answers against the answer key and try to understand any mistakes you made. ◆ Complete a module before doing the corresponding review exercises. Doing these exercises without referring to the lesson you have just completed is a better way to prepare for the final examination. Self-evaluation Activity The purpose of the self-evaluation activity is to help you prepare for the final examination. Before you tackle the self-evaluation activity, reread your notes to ensure you have covered all the material pertaining to the learning objectives cited at the beginning of each module. Make sure you understand the learning objectives. Then do the self-evaluation activity without referring to the main body of the guide or the summaries. Compare your answers with those in the answer key and review any areas you had difficulty with. Materials Have all the materials you need close at hand. ◆ Learning materials: this guide and a notebook in which you will summarize important concepts relating to the learning objectives for each module. ◆ Reference materials: a dictionary. ◆ Miscellaneous materials: a calculator, a pencil for writing your answers and your notes in this guide, a coloured pen for correcting your answers, a highlighter (or a pale-coloured felt marker) to highlight important ideas, a ruler, an eraser, etc. VIII © SOFAD Introduction TABLE OF CONTENTS ◆ ANSWER KEY Evaluation In order to earn the two credits for this course and towards your Secondary School Diploma, you must score at least 60% on a supervised examination dealing with the learning objectives outlined in this guide and administered in an adult education centre. The two-hour written examination counts for 100% of the final course mark. The examination will consist of multiple-choice questions and shortanswer questions. ◆ Succeeding at Distance Learning Work Pace A few tips for organizing your time are given below: ◆ Set up a study schedule that takes into account your availability, your needs and your family and work obligations. ◆ Try to devote a few hours a week to the course, preferably in blocks of two hours. ◆ As much as possible, stick to the schedule you have established. Your Tutor Your instructor is the person who will give you any help you need throughout this course. He or she is available to answer your questions and correct and comment on your assignments. Don’t hesitate to contact your instructor if you are having difficulty with the theory or the exercises, or if you need some words of encouragement to help you get through this course. Information about how to contact your instructor that is not already contained in this guide will be made available to you. Write out your questions and get in touch with your instructor during his or her available hours. If necessary, write to him or her. Your instructor will guide you in your work and provide you with the advice, constructive criticism and support that will help you succeed in this course. Homework Assignments This guide is sold with three homework assignments designed solely for distance learning students. The homework assignments are to be completed at the end of each of the three sections that make up this guide. These assignments will show your tutor whether you understand the subject matter and are ready to go on to the next part of the course. If your tutor feels you are not ready to move on, he or she will indicate this on your homework assignments, providing comments and suggestions to help you get back on track. It is important that you read these corrections and comments carefully. Do your homework assignments without referring to the learning guide and take note of your tutor’s corrections so that you can make any necessary adjustments. This is also an excellent way to prepare for the final examination. Remember not to send in the next assignment until you have received the corrections for the previous one. © SOFAD IX Introduction TABLE OF CONTENTS ◆ ANSWER KEY The Transmission of Hereditary Characteristics What do blond, black or brown hair, curly hair, eye colour, and the shape of the nose and ears have in common? They are all characteristics, or traits, that are transmitted from one generation to the next. While leafing through family photo albums, people often comment on the resemblances they see—or don’t see—between parents and their children: “Sylvia has blond hair, yet both her mom and dad have jet black hair!” Although resemblances among family members have been noticed since the beginning of time, it was the work of Gregor Mendel (1822-1884) that provided the first real insight into heredity, that is, the transmission of biological information, or family traits, from parents to offspring. While all children resemble their parents, in no way are they a carbon copy. Over time, the study of heredity and the expression of hereditary characteristics in individuals gave rise to the science of genetics. Biology Course BLG 5065-2, The Transmission of Hereditary Characteristics, will enable you to expand your knowledge of such topics as the mechanisms of heredity, cross-breeding, the genetics of blood types, sex chromosomes, hereditary diseases, and the causes and effects of certain mutations. Course Outline General Introduction Section 1 – The Mechanisms of Heredity Module 1 Module 2 Cell Basics Cell Division Assignment 1 Section 2 – The Laws of Heredity Module 3 Module 4 Mendel’s Experiments Crossbreeding Assignment 2 Section 3 – Health Problems Related to Heredity Module 5 Module 6 The Heredity of Blood Types Sex Chromosomes, Mutations and Hereditary Diseases ✁ Assignment 3 General Conclusion Self-evaluation Activity X © SOFAD TABLE OF CONTENTS ◆ ANSWER KEY Reader’s Comments The Transmission of Hereditary Characteristics (February 2010) SOFAD is committed to providing course materials adapted to your needs, and we value your opinion. Please write your comments, questions or suggestions on this sheet, or contact us by phone, fax or email. If you find any errors, ambiguities, typographical errors, etc., we would appreciate hearing from you. Thank you for giving us your feedback. Alain Pednault Project Coordinator, Sciences and Technology Tel.: (514) 529-2193 2200, rue Sainte-Catherine Est Fax: (514) 529-2190 Montréal (Québec) H2K 2J1 Email: [email protected] Comments: From: _________________________________________________________________________________________________________________ ✁ School Board: ______________________________________________________________________________________________________ Student: Other: ❑ ❑ Tutor: ❑ Specify: ______________________________________________________________________________________________ ANSWER KEY TABLE OF CONTENTS Section 1 The Mechanisms of Heredity At the end of the 19th century, Mendel conducted conclusiv experiments on the transmission of conclusive hered hereditary characteristics. It was not until the 20t 20th century, however, that understanding of the mechanisms of heredity was p possible thanks to knowledge acquired about cells, chromosomes and genes. By the end of this section, you will be able to explain the mechanisms of heredity. T This section is divided into two modules. The first, entitled Cell Basics, deals with the cell, the nucleus, chromosomes, genes and the stru structure of cellular proteins. The second, entitled Cell Division, explains how genetic material is transmitted from one cell to another during the formation and growth of sex cells, which are essential for reproduction. © SOFAD © SOFAD TABLE OF CONTENTS Module 1 u ANSWER KEY Food for Thought Can we select specific traits for our offspring through genetic CELL manipulation? Can genes be transferred from one species to another species? If your parents could have chosen specific BASICS traits for you, do you think your life would be any different? What is the basis of heredity for living beings? Start pondering these questions now, as you will be asked to state your views at the end of this section. The Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Genes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.16 © SOFAD 1.1 Module 1 – Cell Basics TABLE OF CONTENTS u ANSWER KEY What I Already Know In the 21st century, basic knowledge about the transmission of hereditary characteristics is part of general culture in industrialized countries. This knowledge allows us to understand critical discoveries that influence our beliefs, our social values and our health. The purpose of this exercise is to help you determine what you already know, and identify topics with which you are less familiar. You will come back to it at the end of the module. This will allow you to assess your progress. Answer the following questions in your own words, using one or two sentences. Write what you know. 1. What is responsible for the transmission of hereditary characteristics? 2. Is it heredity or the environment that shapes how an organism will develop? 3. Can you give an example of one type of human cell? 4. Why has it become so important to collect DNA samples at crime scenes? 1.2 © SOFAD Lead-in TABLE OF CONTENTS u ANSWER KEY Objectives of the Module After completing this module, you will be familiar with the biological basis for heredity, thanks to the activities you will be working through in the following two units: The Cell and Genes. More specifically, you will be able to: u associate the cell nucleus, chromosomes and DNA with the transmission of hereditary characteristics; u describe the structure of a chromosome and a gene. © SOFAD 1.3 Module 1 – Cell Basics TABLE OF CONTENTS ANSWER KEY The Cell uIntroduction All living beings are composed of cells. Each type of cell plays a specific role. For example, the human body uses muscle cells for movement, white blood cells to fight off microbes, and nerve cells to control its vital functions. There are approximately 200 types of cells in the human body. Cells behave in the same manner as the body as a whole; they need food to survive, they transform food into cellular structures, they develop and communicate with one another, and they also reproduce and die. The muscle fibre, white blood cell and brain neuron shown below are three types of cells found in the human body. All of these activities are carried out according to a blueprint that is passed on from one generation to the next. In this unit, we will examine the overall structure of a cell and cell nucleus. We will also describe what role the nucleus plays in the transmission of hereditary characteristics. You will learn about the components of a cell, about chromosomes and about the structure of DNA. 1.4 © SOFAD The Cell TABLE OF CONTENTS u ANSWER KEY The Organization of Living Organisms Living organisms vary in their complexity. The most complex organisms have systems of organs made of different types of tissue adapted to their specific functions. Identify the various tissues found in different parts of the human body. E B C Epidermis A-Cartilage B-Epidermis C- Muscle tissue D D-Blood E- Nervous tissue A A- Cartilage is a flexible tissue and less rigid than bone. Like bone, cartilage contains very few cells. The ear and the nose are good examples of cartilage. Cartilage forms the “disks” between the vertebrae and plays a protective role in joints such as the knee. B- The epidermis is the outermost layer of the skin. Epidermal cells are under constant “assault” from the environment, but rapid renewal of the epidermis compensates for the loss of cells on the skin’s surface. C- Muscle tissue is composed of elongated cells called fibers. Their elongated shape makes it easier for them to contract in response to a nerve impulse. D- Blood is about 55% liquid (plasma) and 45% blood cells. The majority of cells are red blood cells (containing hemoglobin), which carry oxygen. Blood also contains white blood cells, which provide protection against microbes. E- Nervous tissue is composed mainly of neurons, or nerve cells. The long, slender projections of nerve cells are called axons. Many axons make up a nerve. © SOFAD 1.5 Module 1 – Cell Basics ANSWER KEY TABLE OF CONTENTS Quick Check 1.1 Which of the following is a tissue. qblood q the knee q q the brain the liver 1.2 Which of the following is an organ? q q q a red blood cell a muscle fiber a stomach Validate with the answer key. Recap In the beginning, there is only one cell. This cell divides and the thousands of cells that are produced specialize and form different types of tissue. Organs are made of different types of tissue adapted to their specific functions. Organs are grouped into systems that allow the organism to adapt efficiently to its environment. u The Components of a Cell Every living organism is composed of cells. Each cell has several components that perform different functions and ensure the cell’s survival. Identify the essential components of a cell and discover their functions. D B C E A- Cell membrane B-Cytoplasm G C-Nucleus D- Mitochondria F E-Ribosomes F- Endoplasmic reticulum G- Golgi complex D H-Centrosome A E H A- The semi-permeable cell membrane (also called the plasma membrane) controls the concentration of nutrients and waste in the cytoplasm. 1.6 © SOFAD The Cell ANSWER KEY TABLE OF CONTENTS B- The cytoplasm is essentially a thick liquid substance. It contains specialized structures, called organelles*, that perform different functions enabling the cell to carry out vital life processes. C- The nucleus contains most of the cell’s genome. The nucleus is referred to as the control centre of the cell because it controls all of its activities. D- The number of these organelles in a cell depends on what the cell needs to do. They are the powerhouses of the cell in that they use the oxygen provided by blood circulation to create cell energy. E- These cellular structures are the protein builders of the cell. Proteins are the cell’s tools and are synthesized using information contained in the genetic code. F- A network of canals that runs through the entire cytoplasm. Proteins synthesized by ribosomes enter the endoplasmic reticulum. G- Proteins synthesized by the cell reach the Golgi complex through the endoplasmic reticulum. There, they are processed, stored or sent to the required destination in order to play a specific role. H- Centrosomes are regions of the cell that produce the microtubules enabling chromosomes to move to opposite ends of the nucleus during cell division. Quick Check 1.3 To which person in a large company would you compare the cell nucleus? q q the lawyer the accountant q q the big boss the maintenance manager 1.4 Which of the following cell structures is involved in cell division? q q centrosome q cell membrane cytoplasm Validate with the answer key. Recap The cell nucleus contains the genetic material responsible for the synthesis and operation of all cell structures. The human body has several million cells, each containing within its nucleus all the genetic information needed to build and support the functions of the entire organism. A single cell is all that is needed to make a completely new you! * © SOFAD Words appearing in small caps are defined in the glossary at the end of this guide. 1.7 Module 1 – Cell Basics TABLE OF CONTENTS u ANSWER KEY The Cell Nucleus The nucleus houses the cell’s genetic material. Let us examine what form this genetic material takes in the nucleus. DNA Cell membrane Nucleosome (bead) Chromatin (in the nucleus) Nuclear envelope The genetic material consists of molecules of DNA packaged as chromatin or chromosomes, depending on whether the cell is growing or in the process of dividing. Chromatin has a “beads on a string” appearance. The beads (nucleosomes) consisting of deoxyribonucleic acid (DNA) and proteins (histones) form a core around which the DNA molecule coils. Early in the process of cell division, the chromatin coils, supercoils and becomes more and more compact. This material undergoes a process of segmentation giving rise to chromosomes. Once the cell has divided, the chromosomes decondense to become chromatin strands again. 1.8 © SOFAD The Cell TABLE OF CONTENTS ANSWER KEY uChromosomes Genetic material is generally described as being carried on chromosomes. We will now examine the structure of chromosomes. Chromosomes become visible in the nucleus during cell division. In the illustration below, the chromosome is composed of two strands, called DNA and are joined in the chromatids. Chromatids are composed of identical centromere . When the mother cell divides, each of the two daughter cells that are produced receives one of the two identical chromatids making up each chromosome. © SOFAD 1.9 Module 1 – Cell Basics ANSWER KEY TABLE OF CONTENTS u DNA Structure The DNA molecule has a specific structure that allows it to store and transmit genetic information. It resembles a ladder whose rungs are joined like a zipper. Identify the components of DNA. B Chemical bonds C G A- Analog model A T B- Schematic model G C T A C- Simplified model A C G A T A T C G T A A T G C C A- DNA has a spiral staircase-like structure. The sides of the ladder are composed of hundreds of small blocks called nucleotides. The two sides are joined together like the teeth of a zipper, with the teeth representing the four nitrogenous bases. Each nucleotide is composed of one of the following nitrogenous bases: adenine (A), thymine (T), guanine (G), cytosine (C). B- This model of the same molecule shows two chains of nucleotides, composed of a nitrogenous base (A, T, G, C), a sugar (in red) and a phosphate (in green). The illustration shows how nucleotides containing nitrogenous bases join the two open chains. The shapes of the nitrogenous bases are complementary. Adenine can bind only with thymine (A-T) and guanine can bind only with cytosine (G-C). C- The simplified model shows a ladder whose rungs are formed of either an A-T pair or a G-C pair. The sides represent the two nucleotide chains. 1.10 © SOFAD The Cell ANSWER KEY TABLE OF CONTENTS Quick Check 1.5 In a DNA molecule, what joins the two sides of the ladder? q q nitrogenous bases nucleotides q genes qproteins 1.6 What encodes genetic information? q q the A-T and G-C pairs q the nucleotides facing each other the order in which the nitrogenous bases are arranged on a chain Validate with the answer key. Recap The DNA molecule consists of two chains of nucleotides. Genetic information is determined by the properties of one of the three components of a nucleotide: the nitrogenous base. There are four nitrogenous bases: adenine, thymine, guanine, cytosine. The order in which the nitrogenous bases are arranged encodes genetic information. u Did You Know? Human cells contain 46 chromosomes (23 pairs). If the DNA from all 46 chromosomes that make up the human genome were laid out end to end, it would stretch about two metres, or more than six feet! The number of chromosomes varies between species. Fruit flies have only 4 pairs of chromosomes, horses have 32 pairs, and dogs, 39 pairs! 2 meters © SOFAD 1.11 Module 1 – Cell Basics TABLE OF CONTENTS u ANSWER KEY Complementary Bases Nitrogenous bases follow base-pairing rules. Correctly match the four nitrogenous bases below. A C C G C A A G T C G T C Validate with the answer key. A A G A- Adenine forms a complementary base pair with thymine. G- Guanine forms a complementary base pair with cytosine. C- Cytosine forms a complementary base pair with guanine. T- Thymine forms a complementary base pair with adenine. Recap On complementary DNA strands, adenine is always paired with thymine and guanine is always paired with cytosine. Adenine also pairs with another nitrogenous base called uracil. In RNA, or ribonucleic acid, uracil (instead of thymine) pairs with adenine. 1.12 © SOFAD The Cell TABLE OF CONTENTS u ANSWER KEY Did You Know? The human genome is composed of 3.2 billion base pairs. The sequence of nitrogenous bases (adenine, thymine, guanine and cytosine) that make up the long nucleotide chains of our DNA allows for all the variations contained in tens of thousands of genes. Imagine the genome is a book. The information it contains would be equivalent to that in about 1000 telephone books. As impressive as it is, the human genome is small compared with that of an organism called Amoeba dubia. This unicellular organism has a genome containing a record 670 billion base pairs! That is at least 200 times larger than the human genome. © SOFAD 1.13 Module 1 – Cell Basics TABLE OF CONTENTS u ANSWER KEY The Cell and Its Nucleus The cell, the nucleus and the chromosomes are the basic building blocks of life. Review some related terminology by completing the following crossword puzzle. 1 C H 2 C R O M 3 4 C A T I 5 E N Validate with the answer key. 1- Segments of condensed, tightly folded and coiled chromatin. 2- The constricted region joining the two sister chromatids that make up an X-shaped, or double, chromosome. 3- It is part of a DNA nucleotide and pairs with thymine. 4- Each chromosome contains two, identical ones. During DNA replication, one of them serves as a model for the other. 5- It surrounds the nucleus and controls the exchange of substances between the nucleus and the cytoplasm. Recap At the beginning of the 20th century, research on the cell and the nucleus advanced by leaps and bounds. During the 1950s, the discovery of DNA in the cell nucleus paved the way for achieving understanding of where genetic information is stored and how this information is passed from one cell to its progeny during the growth of an organism. 1.14 © SOFAD The Cell TABLE OF CONTENTS ANSWER KEY uConclusion The column headings in the following table are related to topics covered in this unit. Fill in the blank spaces with the appropriate terms from the list to the right of the table. CHROMOSOME CELL DNA Centromere Chromatid Ribosomes Nucleus Validate with the answer key. Nucleotides AT and GC Recap The cell is the basic unit of life. The human body has 200 different types of specialized cells that make up the tissues of the various organs. The DNA in the nucleus of each cell makes up the genome of the organism. The human genome consists of 23 pairs of chromosomes: each chromosome consists of a DNA molecule composed of roughly 200 million pairs of nucleotides. This genetic information ensures that hereditary characteristics are preserved and passed on. End of unit Before you continue, go to the “Unit Summaries” section and complete the corresponding review activity. © SOFAD 1.15 Module 1 – Cell Basics TABLE OF CONTENTS ANSWER KEY Genes uIntroduction Gene for iris colour A T C G T A A T G C The DNA in the cell nucleus makes up the genetic material (i.e., genome) of all living organisms. Hereditary characteristics, or traits, are encoded in nucleotide sequences hundreds of base pairs long. These DNA sequences are genes. Cells of various types carry out different functions. The cell carries out two vital tasks: it copies its genes so that a set can be passed on to each daughter cell during cell division and it uses its genes to synthesize proteins that are involved in the expression of hereditary traits. In this unit, we will examine the mechanism of DNA replication in the nucleus and the mechanisms by which the information carried by a gene is expressed. 1.16 © SOFAD Genes ANSWER KEY TABLE OF CONTENTS uGenes A chromosome carries thousands of genes, each of which contains a specific sequence of nucleotide base pairs. Now we will look at the differences and similarities between genes. A T C G C G G C C G A T A T G C C G A T T A G C 2 1 4 3 G C G C A T G C A T A T A T G C C G C G T A T A A portion of gene 1 = A-C-C-G-C-A-A-G-C-A-T-G A portion of gene 2 = A-C-C-G-C-A-A-G-C-A-T-G A portion of gene 3 = G-G-A-G-A-A-A-G-C-C-T-T A portion of gene 4 = G-G-A-G-A-A-A-G-C-C-T-T © SOFAD 1.17 Module 1 – Cell Basics TABLE OF CONTENTS ANSWER KEY Quick Check 1.7 Why are genes 1 and 2 and genes 3 and 4 identical? q q q the sister chromatids from the same chromosome come from a single parent the cell copied one of the chromatids from the other both parents passed on the same genes 1.8 Would replacing one nitrogenous base by a different base on a gene have an effect? q q q such a subtle change would have no effect changing a single base modifies the information and so has an effect changing three nitrogenous bases would have an effect 1.9 Which of the following three statements do you agree with? q q each sister chromatid from the same chromosome carries its own genes each sister chromatid from the same chromosome carries half the genes contained in a chromosome q each sister chromatid from the same chromosome carries the same genes in the same order Validate with the answer key. Recap The specific order in which nucleotide base pairs are arranged encodes genetic information. A gene is an ordered sequence of nucleotides that encodes the information needed to synthesize a specific protein and express a particular hereditary trait. Some genes do not carry hereditary information; they act as switches by turning gene expression on or off. uAlleles Humans have 23 pairs of chromosomes. One chromosome in each pair is contributed by the father and one by the mother. For any given trait, there are two sources of information: the gene passed on by the mother and the gene passed on by the father. These genes are the two alleles that control specific traits, for example, eye or hair colour. For each hereditary trait, one 1.18 allele is paternally derived and the other is maternally derived. © SOFAD Genes ANSWER KEY TABLE OF CONTENTS u Copying a Gene With a few exceptions, every cell in your body contains a complete copy of your genome, or roughly 30 000 genes. A cell generally uses only the genes it needs to function and deactivates the rest. In the next 60 seconds, your body will produce enough new DNA that, if linked together, it would stretch 100 000 km, or the average distance a car travels in five years. The cell must have the ability to keep genetic information intact, for its own benefit and for that of its progeny. The genes in a cell must be copied in order to preserve and transmit information from one cell to another. u DNA Replication Before a cell can divide it must first make a copy of its DNA. In each box below, write the uppercase letter representing the base that pairs with the nitrogenous base indicated. A C C G C A A G C A T G A C C G C A A G C A T G Validate with the answer key. In DNA replication, new strands of DNA are copied through complementary base pairing. This dynamic process requires the action of proteins called enzymes. These are the cell’s tools. © SOFAD 1.19 Module 1 – Cell Basics ANSWER KEY TABLE OF CONTENTS u Find Out More - DNA Replication This material is not covered in the course. A T DNA replication by complementary pairing of C G a new DNA strand is constructed from one of G C T nitrogenous bases is the mechanism whereby the two chains of the original DNA sequence. This process requires the help of proteins A called enzymes. Click on the following link C http://cours1.sofad.qc.ca/ressources/fichiers/ to watch an animation of DNA replication: BLG_5065_webography.html G u From Genes to Hereditary Characteristics In general, it is easy to distinguish individuals by their facial features, or physiognomy. Physiognomy is the outward expression of each person’s specific genome, which is found in the cell nucleus. A photograph of an individual’s genome is equivalent to Hair the main component of hair fibre is keratin a photograph of his or her face. A hereditary characteristic can be observed only at the level of tissues or organs, but genes express themselves only at the cellular level. Kidneys renin controls blood pressure How is a gene expressed at the cellular level? Salivary glands amylase in the saliva breaks down sugar like starch in bread Red blood cells hemoglobin carries oxygen Muscles myosin is responsible for contraction Gene expression occurs through the synthesis of different proteins. Each protein within the body has a specific function. Some proteins serve as construction materials (structural proteins), while others act as catalysts (enzymes). Hormones and antibodies are also proteins. The human body needs 20 amino acids to synthesize the thousands of proteins it uses. 1.20 © SOFAD Genes ANSWER KEY TABLE OF CONTENTS u Find Out More - Protein Construction This material is not covered in the course. DNA molecule Genons A C C C G A A G C A T G DNA strand Transcription mRNA U G G G C U U C G U A C Codons Translation Amino acids Tryptophan Arginine Serine Tyrosine Protein How do cells go about building proteins? Proteins are synthesized on the ribosomes found in the cell cytoplasm. 1. DNA carries genetic information on segments called genes and is enclosed in the cell nucleus. 2. The cell transcribes, or transfers, the genetic information to a strand of messenger RNA (mRNA). This process is called transcription. The mRNA carries the genetic information out of the nucleus to the ribosomes. 3. The amino acids encoded in the mRNA are transported to the ribosomes. Transfer RNA, or tRNA (not shown), are molecules that bind to and carry specific amino acids, of which there are 20, to the ribosomes and places them opposite a mRNA codon. 4. The amino acids must be assembled in the order determined by the mRNA. Each tRNA molecule carries an anticodon that is complentary to a specific codon of mRNA on the ribosome. When a given codon and anticodon pair up, the ribosome removes the amino acid from the tRNA. This process is called translation. A protein can consist of between 100 and 300 amino acids. Visit http://cours1.sofad.qc.ca/ressources/fichiers/BLG_5065_webography.html to see an animation of cell protein construction. © SOFAD 1.21 Module 1 – Cell Basics TABLE OF CONTENTS u ANSWER KEY DNA, Genes, Alleles and Chromosomes The four terms in the table below are related. Match each description in the right-hand column with the corresponding term in the left-hand column by drawing a line between them. DNA Made up of DNA and histone proteins, it carries several genes. GENE A giant molecule composed of two chains of nucleotides. There are four different nucleotides, each of which has a different nitrogenous base. CHROMOSOME One of two alternative forms of a gene (one from the father and one from the mother) specifying an inherited characteristic. ALLELE A sequence of DNA nucleotides that occupies a specific site on a chromosome. This sequence serves as a template for the synthesis of a specific protein. Validate with the answer key. Recap Each chromosome is composed of DNA, specific segments of which serve to synthesize cell proteins. These segments of DNA are genes. Genes can either carry or control inherited characteristics. In living organisms that reproduce sexually, like humans, chromosomes exist in pairs. Each inherited characteristic, such as eye colour, is determined by two variants of a specific gene, one from the father’s chromosome and the other from the mother’s chromosome. Thus, a pair of chromosomes contains a paternal allele and a maternal allele, the two versions of the gene that controls a given hereditary trait. 1.22 © SOFAD Genes ANSWER KEY TABLE OF CONTENTS u Did You Know? We have more in common with other living beings than we could ever imagine! In their genome, individuals have traces of ancient genes stemming from the beginning of time that they share with every living organism. What do you have in common with a MONKEY or a MOUSE? Find out more at: http://cours1.sofad.qc.ca/ressources/fichiers/ BLG_5065_webography.html u Example: Chromosome 7 Several genes located on human chromosomes have been mapped. Identify some of the genes on chromosome 7. Osteoporosis 1 1- NUMBER OF GENES 1443 genes 2 Colon cancer 2- GENES AND DISEASES 3- GENE FOR COLOUR BLINDNESS Colour blindness 3 1- Genes occupy specific spots, or loci, on a chromosome. To date, 1443 genes have been identified on chromosome 7. 2- Although genes work together in complex ways to keep our bodies functioning properly, some alleles have defects that can result in disease. Several genes on chromosome 7 predispose to disease. Osteoporosis and colon cancer are two examples. 3- Many colour blind people have a defective perception of red and green. This deficiency is caused by an abnormality in the structure of the retina. The gene that codes for blue pigment is located on chromosome 7. The other two genes involved in colour blindness, those coding for red and green pigments, are located on the X chromosome. © SOFAD 1.23 Module 1 – Cell Basics TABLE OF CONTENTS u ANSWER KEY A Silk Goat! What is a GMO? A genetically modified organism (GMO) is a plant, animal or microorganism whose genetic code has been altered in order to give it characteristics that it does not have naturally. Scientists can now transfer genes between species that otherwise would be incapable of mating, for example, a goat and a spider. Find out more at: http://cours1.sofad.qc.ca/ressources/fichiers/BLG_5065_ webography.html u DNA and Genes Genes are located on chromosomes. What concepts are used to define a gene and its role in the transmission of inherited characteristics? Review these concepts by completing the following crossword puzzle. 1 C H 2 P R O M O 3 A S O M 4 5 G G Validate with the answer key. E S 1- A function of genes that are not carriers of hereditary characteristics. 2- Each carrier gene expresses itself by synthesizing these. 3- A pair of genes that determine the same characteristic and that are provided by each parent. 4- Each chromosome contains hundreds of these. 5- Small segments of a DNA molecule that express hereditary characteristics. 1.24 © SOFAD Genes TABLE OF CONTENTS ANSWER KEY Recap Cell activities are regulated by the expression of the genes located on the chromosomes, i.e., the alleles received from both parents. Genes express themselves by synthesizing proteins on the cell’s ribosomes. Not all genes are carriers of inherited characteristics; some control cell activities. Depending on its needs, the cell can switch genes on or off. uConclusion The column headings in the following table are related to topics covered in this unit. Fill in the blank spaces with the appropriate terms from the list to the right of the table. GENE CHROMOSOME PROTEINS Chromatids Insulin Sequence of nucleotides Amino acid Validate with the answer key. Alleles Centromere Recap Cells carry out two vital tasks related to genes. First, they accurately copy the genes prior to cell division. Second, they translate the information encoded in the genes by making thousands of proteins. End of unit Before you continue, go to the “Unit Summaries” section and complete the corresponding review activity. © SOFAD 1.25 Module 1 – Cell Basics TABLE OF CONTENTS u ANSWER KEY What I Know Now At the beginning of this module, you answered four questions about the learning content of each of the two units to the best of your knowledge. Here are the same questions. Answer them again, then compare your answers to your previous ones. 1. What is responsible for the transmission of hereditary characteristics? 2. Is it heredity or the environment that determines how an organism will develop? 3. Can you give an example of one type of human cell? 4. Why has it become so important to collect DNA samples at crime scenes? 1.26 © SOFAD Wrap-up TABLE OF CONTENTS u ANSWER KEY Share Your Opinion Given what you have learned about the cell and genes, you should now be able to understand the social issues related to genetically modified organisms. If it were possible to alter the human genome, would you want to select hereditary characteristics that could be passed on to your children? q Yes qNo q I don’t know Recap More and more people are turning to plastic surgery (e.g., facelifts), a wide range of medications, hormones and nutritional supplements to enhance their appearance or their performance, or to simply improve their quality of life. Now that researchers have identified the location of certain defective genes on human chromosomes, work is under way on approaches for inserting new, functional genes or for repairing defective ones. This is called gene therapy. Although the technology is still in its infancy, it holds considerable promise. uQuiz 1. Living organisms vary in their complexity. The most complex are composed of systems of organs consisting of different types of tissue adapted to the function of each organ. Which of the following is a type of tissue? A.cartilage B. the liver C. the knee D. the brain 2. What am I? In the cell, I contain specialized structures called organelles, which carry out the various tasks that ensure proper functioning of the cell. A. the nucleus B. mitochondria C. cytoplasm D. a ribosome 3. What am I? In the cell, I serve as the assembly site for cellular proteins, which are synthesized from the information in the genome. A. the endoplasmic reticulum B. the Golgi complex C. a ribosome D. the centrosome © SOFAD 1.27 Module 1 – Cell Basics TABLE OF CONTENTS ANSWER KEY 4. The genome is contained in the cell nucleus. The form in which the genome exists in the cell can be described in different ways. Which of the following statements is true? A. Chromatin is composed of chromatids. B. A chromosome is composed of one chromatid and two centromeres. C. A chromatid is composed of 46 strands of chromatin. D. A chromosome consists of a DNA molecule and proteins called histones. 5. DNA and the cell. Which of the following statements is false? A. DNA is contained in the nucleus and cannot leave it. B. Only chromosomes (not chromatin), once formed, are made up of DNA. C. There are 46 DNA molecules in a cell. D. DNA consists of two chains of nucleotides. 6. How is a gene represented in a cell? A. by each DNA base pair B. by a nitrogenous base pair, A-T or G-C C. by a sequence of DNA base pairs D. by a group of three base pairs out of four 7. How is a gene expressed in a cell? A. by protein synthesis B. by the synthesis of alleles C. by DNA replication D. by the transformation of chromatin into a chromosome 8. What roles do genes play? A. They transform chromatin into chromosomes. B. They carry genetic information or control the activity of other genes. C. They form the ribosomes. D. They join the chromatids together. 9. Which of the following statements is true? A. A chromosome contains hundreds of different genes. B. A hereditary characteristic is determined by an allele from one parent. C. The cell nucleus contains only the DNA necessary for the activities of a single cell. D. It is impossible to add genes to or to alter the genome of a living being. 1.28 © SOFAD Wrap-up TABLE OF CONTENTS ANSWER KEY 10.All living organisms are composed of cells. How many types of cells are there in the human body? A. The human body has only one type of cells: human cells. B. There are 200 types of cells grouped into tissues. C. There are 2000 types of cells grouped into different organs. D. Each organ in the human body has its own type of cells. Validate with the answer key. © SOFAD 1.29