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Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Section Summary Mendel’s Work Key Concepts ■ What were the results of Mendel’s experiments, or crosses? ■ What controls the inheritance of traits in organisms? Heredity is the passing of physical characteristics from parents to offspring. Gregor Mendel was curious about the different forms of characteristics, or traits, of pea plants. Mendel’s work was the foundation of genetics, the scientific study of heredity. A new organism begins to form when egg and sperm join in the process called fertilization. Before fertilization can happen in pea plants, pollen must reach the pistil of a pea flower through pollination. Pea plants are usually self-pollinating, meaning pollen from a flower lands on the pistil of the same flower. Mendel developed a method by which he cross-pollinated, or “crossed,” pea plants. Mendel crossed two pea plants that differed in height. He crossed purebred tall plants with purebred short plants. These parent plants, the P generation, were purebred because they always produced offspring with the same trait as the parent. In all of Mendel’s crosses, only one form of the trait appeared in the F1 generation. However, in the F2 generation, the “lost” form of the trait always reappeared in about one fourth of the plants. From his results, Mendel reasoned that individual factors, one from each parent, control the inheritance of traits. Today, scientists call the factors that control traits genes. The different forms of a gene are called alleles. An organism’s traits are controlled by the alleles it inherits from its parents. Some alleles are dominant, while other alleles are recessive. A dominant allele is one whose trait always shows up in the organism when the allele is present. A recessive allele is hidden whenever the dominant allele is present. A trait controlled by a recessive allele will only show up if the organism does not have the dominant allele. In Mendel’s cross, the purebred tall plant has two alleles for tall stems. The purebred short plant has two alleles for short stems. The F 1 plants are all hybrids: they have two different alleles for the trait—one allele for tall stems and one for short stems. Geneticists use a capital letter to represent a dominant allele and a lowercase version of the same letter for the recessive allele. Mendel’s discovery was not recognized during his lifetime. In 1900, three different scientists rediscovered Mendel’s work. Because of his work, Mendel is often called the Father of Genetics. © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Guided Reading and Study Mendel’s Work This section describes how Gregor Mendel identified the method by which characteristics are passed from parents to their offspring. Use Target Reading Skills As you read, complete the outline about Mendel’s work. Use the red headings for the main idea and the blue headings for the supporting ideas. I. Mendel’s experiments A. crossing pea plants B. C. D. II. A. B. C. D. Introduction 1. Gregor Mendel experimented with hundreds of pea plants to understand the process of ________________________. Match the term with its definition. Term ____ 2. heredity Definition a. The scientific study of heredity ____ 3. genetics b. Physical characteristics ____ 4. traits c. The passing of traits from parents to offspring Mendel’s Experiments In a flower, the female sex cells, or eggs, are produced by the ________________________. Pollen, which contains the male sex cells, is produced by the ________________________. 6. What are purebred organisms? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Genetics: The Science of Heredity 5. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity Mendel’s Work ■ Guided Reading and Study (continued) 7. Complete the flowchart below, which summarizes Mendel's first experiment with pea plants. Mendel's Experiment Purebred tall plants are crossed with purebred F1 offspring are all plants. . F1 offspring are allowed to self-pollinate. F2 offspring are and . 8. Circle the letter of other traits in garden peas that Mendel studied. a. seed size, seed shape, seed color b. seed color, pod color, flower shape c. flower size, pod shape, seed coat color d. pod color, seed shape, flower position 9. Two forms of the trait of seed shape in pea plants are ________________________ and ________________________. Dominant and Recessive Alleles 10. Circle the letter of each sentence that is true about alleles. a. Recessive alleles are never present when dominant alleles are present. b. Alleles are different forms of a gene. c. A trait controlled by a dominant allele always shows up in the organism when the allele is present. d. Recessive alleles hide dominant alleles. 11. Is the following sentence true or false? Only pea plants that have two recessive alleles for short stems will be short. ________________________ © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Guided Reading and Study Match the pea plant with its combination of alleles. Pea Plant Combination of Alleles ____ 12. purebred short a. Two alleles for tall stems ____ 13. purebred tall b. One allele for tall stems and one allele for short stems ____ 14. hybrid tall c. Two alleles for short stems 15. A dominant allele is represented by a(n) ________________________ letter. 16. A recessive allele is represented by a(n) ________________________ letter. 17. How might a geneticist write the alleles to show that a tall pea plant has one allele for tall stems and one allele for short stems? ________________________ 18. Is the following sentence true or false? Some scientists during Mendel's time thought Mendel should be called the Father of Genetics. ________________________ Genetics: The Science of Heredity © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Review and Reinforce Mendel’s Work Understanding Main Ideas Study the diagram. Then answer the following questions on a separate sheet of paper. P Generation F1 Generation × 1. 2. 3. 4. 5. F2 Generation × What trait in pea plants is being studied in the cross above? What are the two alleles of this trait? Which allele is the dominant allele? Explain how you know. Which allele is the recessive allele? Explain. What alleles do the F1 offspring have? Explain which allele was inherited from which parent. Building Vocabulary Match each term with its definition by writing the letter of the correct definition on the line beside the term. a. the passing of traits from parents to offspring ____ 6. genetics ____ 7. alleles ____ 8. traits ____ 9. recessive allele ____ 10. genes b. an organism with two different alleles for a trait c. factors that control traits d. physical characteristics of organisms ____ 11. hybrid ____ 12. heredity e. an allele whose trait always shows up in the organism ____ 13. dominant allele f. the different forms of a gene g. the scientific study of heredity h. an allele whose trait is masked in the presence of a dominant allele © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Enrich The Test Cross When an organism has a trait controlled by a dominant allele, it can either be a hybrid or a purebred. To find out which, geneticists can use a test cross. In a test cross, the organism with the trait controlled by a dominant allele is crossed with an organism with a trait controlled by a recessive allele. If all offspring have the trait controlled by the dominant allele, then the parent is probably a purebred. If any offspring has the recessive trait, then the dominant parent is a hybrid. Study the test cross below, then answer the questions. Test Cross Test Cross H = short hair h = long hair H = Short hair h = Long hair × Generation PPGeneration hh H ? F1 Generation H ? H ? hh H ? Answer the following questions on a separate sheet of paper. © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Genetics: The Science of Heredity 1. Is the long-haired cat in the P generation a hybrid or a purebred? Explain your answer. 2. Is the short-haired cat in the P generation a hybrid or a purebred? Explain your answer. 3. If the short-haired cat in the P generation were purebred, what would you expect the offspring to look like? 4. In horses, the allele for a black coat (B) is dominant over the allele for a brown coat (b). A cross between a black horse and a brown horse produces a brown foal. Is the black horse a hybrid or a purebred? Explain. 5. In guinea pigs, the allele for a smooth coat (S) is dominant over the allele for a rough coat (s). Explain how you could find out whether a guinea pig with a smooth coat is a hybrid or a purebred. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Skills Lab Take a Class Survey Problem Are traits controlled by dominant alleles more common than traits controlled by recessive alleles? Skill Focus developing hypotheses, interpreting data Materials mirror (optional) Procedure PART 1 Dominant and Recessive Alleles 1. Write a hypothesis reflecting your ideas about the problem question. ________________________________________________________________________ ________________________________________________________________________ 2. For each of the traits listed in the data table on the next page, work with a partner to determine which trait you have. Circle that trait in your data table. 3. Count the number of students in your class who have each trait. Record that number in your data table. Also record the total number of students. PART 2 Are Your Traits Unique? 4. Look at the circle of traits in your text. All the traits in your data table appear in the circle. Place the eraser end of your pencil on the trait in the small central circle that applies to you—either free ear lobes or attached ear lobes. 5. Look at the two traits touching the space your eraser is on. Move your eraser onto the next description that applies to you. Continue using your eraser to trace your traits until you reach a number on the outside rim of the circle. Share that number with your classmates. © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Skills Lab Data Table Total Number or Students ________________________ Trait 1 Number Trait 2 A Free ear lobes Attached ear lobes B Hair on fingers No hair on fingers C Widow’s peak No widow’s peak D Curly hair Straight hair E Cleft chin Smooth chin F Smile dimples No smile dimples Number Analyze and Conclude Write your answers in the spaces provided. 1. Observing The traits listed under Trait 1 in the data table are controlled by dominant alleles. The traits listed under Trait 2 are controlled by recessive alleles. Which traits controlled by dominant alleles were shown by a majority of students? Which traits controlled by recessive alleles were shown by a majority of students? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 3. Developing Hypotheses Do your data support the hypothesis you proposed in Step 1? Write an answer with examples. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Genetics: The Science of Heredity 2. Interpreting Data How many students ended up on the same number on the circle of traits? How many students were the only ones to have their number? What do the results suggest about each person’s combination of traits? ________________________________________________________________________ Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity Take a Class Survey ■ Skills Lab (continued) Design an Experiment Do people who are related to each other show more genetic similarity than unrelated people? Write a hypothesis. Then design an experiment to test your hypothesis. Obtain your teacher’s permission before carrying out your investigation. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Section Summary Probability and Heredity Key Concepts ■ What is probability and how does it help explain the results of genetic crosses? ■ What is meant by genotype and phenotype? ■ What is codominance? Probability is a number that describes how likely it is that an event will occur. The principles of probability predict what is likely to occur, not necessarily what will occur. For example, in a coin toss, the coin will land either heads up or tails up. Each of these two events is equally likely to happen. In other words, there is a 1 in 2 chance that a tossed coin will land heads up, and a 1 in 2 chance that it will land tails up. A 1 in 2 chance can be expressed as a fraction, 1/2, or as a percent, 50 percent. The result of one coin toss does not affect the result of the next toss. Each event is independent of another. When Gregor Mendel analyzed the results of his crosses in peas, he carefully counted all the offspring. Over time, he realized that he could apply the principles of probability to his crosses. Mendel was the first scientist to recognize that the principles of probability can be used to predict the results of genetic crosses. A tool that applies the laws of probability to genetics is a Punnett square. A Punnett square is a chart that shows all the possible combinations of alleles that can result from a genetic cross. Geneticists use Punnett squares to show all the possible outcomes of a genetic cross and to determine the probability of a particular outcome. In a Punnett square, all the possible alleles from one parent are written across the top. All the possible alleles from the other parent are written down the left side. The combined alleles in the boxes of the Punnett square represent all the possible combinations in the offspring. In a genetic cross, the allele that each parent will pass on to its offspring is based on probability. Two useful terms that geneticists use to describe organisms are genotype and phenotype. An organism’s phenotype is its physical appearance, or visible traits. An organism’s genotype is its genetic makeup, or allele combinations. When an organism has two identical alleles for a trait, the organism is said to be homozygous for that trait. An organism that has two different alleles for a trait is said to be heterozygous for that trait. For all of the traits in peas that Mendel studied, one allele was dominant while the other was recessive. This is not always the case. In an inheritance pattern called codominance, the alleles are neither dominant nor recessive. As a result, both alleles are expressed in the offspring. Codominant alleles are written as capital letters with superscripts to show that neither is recessive. © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Guided Reading and Study Probability and Heredity This section explains what probability is and how the laws of probability can be used in the study of genetics. Use Target Reading Skills After you read the section, reread the paragraphs that contain definitions of Key Terms. Use all the information you have learned to write a definition of each Key Term in your own words. Principles of Probability 1. A number that describes how likely it is that an event will occur is called ________________________. 2. Circle the letter of each answer that equals the probability that a tossed coin will land heads up. a. 1 in 2 b. 1/2 c. 50 percent d. 20 percent 3. Is the following sentence true or false? When you toss a coin 20 times, you will always get 10 heads and 10 tails. ________________________ 4. If you toss a coin five times and it lands heads up each time, can you expect the coin to land heads up on the sixth toss? Explain. ________________________________________________________________________ ________________________________________________________________________ Genetics: The Science of Heredity © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Guided Reading and Study Probability and Heredity (continued) Probability and Genetics 5. When Mendel crossed two hybrid plants for stem height (Tt), what results did he always get? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 6. Mendel realized that the principles of probability could be used to ________________________ the results of genetic crosses. 7. A chart that shows all the possible combinations of alleles that can result from a genetic cross is called a(n) ________________________. 8. Write in the alleles of the parents and the possible allele combinations of the offspring in the Punnett square below. (Note that both parents are tall. Three of the offspring are tall and one is short.) © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Guided Reading and Study Phenotypes and Genotypes Match the term with its definition. Term ____ 9. phenotype ____ 10. genotype ____ 11. homozygous ____ 12. heterozygous Definition a. Describes an organism with two identical alleles for a trait b. An organism’s physical appearance, or visible traits c. An organism’s genetic makeup, or allele combinations d. Describes an organism that has two different alleles for a trait 13. Mendel used the term ________________________ to describe heterozygous pea plants. Codominance 14. Is the following sentence true or false? In codominance, the alleles are neither dominant nor recessive. ________________________ 15. In cattle, red hair and white hair are codominant. Cattle with both white hair and red hair are ________________________. Genetics: The Science of Heredity © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Review and Reinforce Probability and Heredity Understanding Main Ideas Complete the two Punnett squares below, and then answer the questions on a separate sheet of paper. 1. Punnett Square A: B 2. Punnett Square B: b B Bb bb b Bb bb 3. In the cross between two black guinea pigs shown in Punnett Square A, what is the probability that an offspring will be black? White? 4. Is it possible that the cross between two black guinea pigs in Punnett Square A would not produce a white guinea pig? Explain. 5. What color are the guinea pig parents in the cross shown in Punnett Square B? 6. Which guinea pig parent(s) in Punnett Square B is homozygous? Which is heterozygous? Explain how you know. 7. Calculate the probability that an offspring will be black in the cross in Punnett Square B. What is the probability that an offspring will be white? Building Vocabulary Match each term with its definition by writing the letter of the correct definition on the line beside the term. ____ 8. heterozygous ____ 9. Punnett square ____ 10. genotype ____ 11. codominance ____ 12. probability ____ 13. homozygous ____ 14. phenotype a. a chart that shows all the possible combinations of alleles that can result from a genetic cross b. a number that describes how likely it is that an event will occur c. an organism that has two identical alleles for a trait d. an organism’s physical appearance e. an organism’s genetic makeup, or allele combinations f. an organism that has two different alleles for a trait g. inheritance pattern in which the alleles are neither dominant nor recessive © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Enrich Genetic Crosses With Two Traits In his work with garden peas, Mendel also set up crosses in which he studied the inheritance of two P Generation traits at one time. For example, he crossed tall plants having green pods (TTGG) with short plants having yellow pods (ttgg). The F1 offspring showed both traits controlled by dominant alleles, tall and green. Mendel allowed the F 1 F1 Generation offspring to self-pollinate. The F2 offspring had four different phenotypes: tall plants with green pods, tall plants with yellow pods, short plants with green pods, and short plants with yellow pods. These results led Mendel to formulate the Law of Independent Assortment, which states that alleles of one gene separate or assort independently of alleles of F2 Generation another gene. In other words, the distribution of alleles of one gene does not affect the distribution of alleles for another gene. Study the Punnett square of a genetic cross between two pea plants with two different traits. Then answer the questions that follow. × TTGG ttgg TtGg TG Tg tG tg TTGG TTGg TtGG TtGg TTGg TTgg TtGg Ttgg TtGG TtGg ttGG ttGg TtGg Ttgg ttGg ttgg TG Tg tG tg Answer the following questions on a separate sheet of paper. © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Genetics: The Science of Heredity 1. What are all the possible combinations of alleles that each F 1 parent can pass on to the offspring? 2. What are the possible genotypes of the F 2 offspring? What are the possible phenotypes of the F 2 offspring? 3. What is the probability that an F2 offspring will be tall with green pods? What is the probability that an F2 offspring will be short with yellow pods? Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Skills Lab Make the Right Call! Problem How can you predict the possible results of genetic crosses? Skills Focus making models, interpreting data Materials 2 small paper bags 3 blue marbles marking pen 3 white marbles Procedure 1. Label one bag “Bag 1, Female Parent.” Label the other bag “Bag 2, Male Parent.” Then read over Part 1, Part 2, and Part 3 of this lab. Write a prediction on another sheet of paper about the kinds of offspring you expect from each cross. PART 1 Crossing Two Homozygous Parents 2. Place two blue marbles in Bag 1. This pair of marbles represents the female parent’s alleles. Use the letter B to represent the dominant allele for blue color. 3. Place two white marbles in Bag 2. Use the letter b to represent the recessive allele for white color. 4. For Trial 1, remove one marble from Bag 1 without looking in the bag. Record the result in your data table. Return the marble to the bag. Again, without looking in the bag, remove one marble from Bag 2. Record the result in your data table. Return the marble to the bag. 5. In the column labeled Offspring’s Alleles, write BB if you removed two blue marbles, bb if you removed two white marbles, or Bb if you removed one blue marble and one white marble. 6. Repeat Steps 4 and 5 nine more times. PART 2 Crossing Homozygous and Heterozygous Parents 7. Place two blue marbles in Bag 1. Place one white marble and one blue marble in Bag 2. 8. Repeat Steps 4 and 5 ten times, and record your data in the data table for Part 2. PART 3 Crossing Two Heterozygous Parents 9. Place one blue marble and one white marble in Bag 1. Place one blue marble and one white marble in Bag 2. 10. Repeat Steps 4 and 5 ten times, and record your data in the data table for Part 3. © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Skills Lab Data Table: Part 1 Trial Allele From Bag 1 (Female Parent) Allele From Bag 2 (Male Parent) Offspring’s Alleles Allele From Bag 2 (Male Parent) Offspring’s Alleles 1 2 3 4 5 6 7 8 9 10 Data Table: Part 2 Trial Allele From Bag 1 (Female Parent) 1 2 3 4 5 6 7 8 9 10 Data Table: Part 3 Trial Allele From Bag 1 (Female Parent) Allele From Bag 2 (Male Parent) Offspring’s Alleles Genetics: The Science of Heredity 1 2 3 4 5 6 7 8 9 10 © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity Make the Right Call! ■ Skills Lab (continued) Analyze and Conclude Write your answers on a separate sheet of paper. 1. Making Models Make a Punnett square for each of the crosses you modeled in Part 1, Part 2, and Part 3. 2. Interpreting Data According to your results in Part 1, how many different kinds of offspring are possible when the homozygous parents (BB and bb) are crossed? Do the results you obtained using the marble model agree with the results shown by a Punnett square? 3. Predicting According to your results in Part 2, what percentage of offspring are likely to be homozygous when a homozygous parent (BB) and a heterozygous parent (Bb) are crossed? What percentage of offspring are likely to be heterozygous (Bb)? Does the model agree with the results shown by a Punnett square? 4. Communicating According to your results in Part 3, what different kinds of offspring are possible when two heterozygous parents (Bb × Bb) are crossed? What percentages of each type of offspring are likely to be produced? Does the model agree with the results of a Punnett square? 5. Inferring For Part 3, if you did 100 trials instead of 10 trials, would your results be closer to the results shown in a Punnett square? Explain. 6. Communicating In a paragraph, explain how the marble model compares with a Punnett square. How are the two methods alike? How are they different? More to Explore In peas, the allele for yellow seeds (Y) is dominant over the allele for green seeds (y). What possible crosses do you think could produce a heterozygous plant with yellow seeds (Yy)? Use the marble model and Punnett squares to test your predictions. © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Section Summary The Cell and Inheritance Key Concepts ■ What role do chromosomes play in inheritance? ■ What events occur during meiosis? ■ What is the relationship between chromosomes and genes? In the early 1900s, scientists were working to identify the cell structures that carried Mendel’s hereditary factors, or genes. In 1903, Walter Sutton observed that sex cells in grasshoppers had half the number of chromosomes as the body cells. He also noticed that each grasshopper offspring had exactly the same number of chromosomes in its body cells as each of the parents. He reasoned that the chromosomes in body cells actually occurred in pairs, with one chromosome in each pair coming from the male and the other coming from the female. From his observations, Sutton concluded that genes are located on chromosomes. He proposed the chromosome theory of inheritance. According to the chromosome theory of inheritance, genes are carried from parents to their offspring on chromosomes. Organisms produce sex cells during meiosis. Meiosis is the process by which the number of chromosomes is reduced by half to form sex cells— sperm and eggs. During meiosis, the chromosome pairs separate and are distributed to two different cells. The resulting sex cells have only half as many chromosomes as the other cells in the organism. When they combine, each sex cell contributes half the number of chromosomes to produce offspring with the correct number of chromosomes. Punnett squares show the results of meiosis. When chromosome pairs separate, so do the alleles carried on the chromosomes. One allele from each pair goes to each sex cell. Chromosomes are made up of many genes joined together like beads on a string. Each chromosome contains a large number of genes, each gene controlling a particular trait. Each chromosome pair has the same genes. The genes are lined up in the same order on both chromosomes. However, the alleles for some of the genes might differ from each other, making the organism heterozygous for some traits. If the alleles are the same, the organism is homozygous for those traits. © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Guided Reading and Study The Cell and Inheritance This section describes how one set of chromosomes from each parent is passed on to the offspring. Use Target Reading Skills As you read, identify the evidence that supports the hypothesis that genes are found on chromosomes. Write the evidence in the graphic organizer below. Evidence Hypothesis Grasshoppers: 24 chromosomes in body cells, 12 in sex cells Chromosomes are important in inheritance. Chromosomes and Inheritance 1. Circle the letter of each sentence that is true about what Sutton observed about chromosome number. a. Grasshopper sex cells have half the number of chromosomes as body cells. b. Grasshopper body cells have half the number of chromosomes as sex cells. c. Grasshopper body cells and sex cells have the same number of chromosomes. d. When grasshopper sex cells join, the fertilized egg has the same number of chromosomes as the body cells of the parents. 2. What is the chromosome theory of inheritance? ________________________________________________________________________ ________________________________________________________________________ Meiosis 3. What is meiosis? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Genetics: The Science of Heredity ________________________________________________________________________ Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Guided Reading and Study The Cell and Inheritance (continued) 4. Complete the cycle diagram, which describes the events that occur during meiosis. Parent cell has four chromosomes pairs. arranged in Sex cells combine to produce offspring. Each offspring has chromosomes, one pair from each parent. Chromosome pairs and are distributed to sex cells. Each sex cell has chromosomes. 5. A Punnett square is a shorthand way to show the events that occur during ________________________. 6. Is the following sentence true or false? During meiosis, the two alleles for each gene stay together. ________________________ 7. If the male parent cell is heterozygous for a trait, Tt, what alleles could the sperm cells possibly have? ________________________________________________________________________ ________________________________________________________________________ A Lineup of Genes 8. How many pairs of chromosomes do human body cells contain? ________________________ 9. How are the genes lined up in a pair of chromosomes? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Review and Reinforce The Cell and Inheritance Understanding Main Ideas Complete the table below by filling in the spaces with the correct stage of meiosis— Beginning, Meiosis I, Meiosis II, End. Event Stage in Meiosis The double-stranded chromosomes move to the center of the cell. The centromeres separate. 1. ________________________ Two cells form, each with half the number of chromosomes. Each chromosome still has two chromatids. 2. ________________________ Four sex cells form with half the number of chromosomes as the parental cells. 3. ________________________ The chromosomes are copied. 4. ________________________ Answer the following questions in the spaces provided. 5. What is the chromosome theory of inheritance? ________________________________________________________________________ ________________________________________________________________________ 6. Why is it important that sex cells have half the number of chromosomes as body cells? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ Building Vocabulary Fill in the blank to complete the statement. 7. The process by which the number of chromosomes is reduced by half to form sex cells is called ________________________. © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Genetics: The Science of Heredity ________________________________________________________________________ Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Enrich A Model of Meiosis Follow the procedure below to make a model of meiosis. Materials different colors of pipe cleaners or yarn beads macaroni string glue scissors marker construction paper or poster board Procedure 1. Study the diagram of the stages of meiosis in your textbook. 2. Decide how you can use the materials listed above, or other materials of your choice, to make a model of meiosis. Your model should include the beginning of meiosis, meiosis I, meiosis II, and the end of meiosis. 3. Create your model. Begin with at least six copied pairs of chromosomes. Label the stages of meiosis and all the important structures. On a separate sheet of paper, write a description in your own words of what happens in each stage of meiosis. Analyze and Conclude Answer the following questions on a separate sheet of paper. What is meiosis? What must happen before meiosis can begin? What happens to chromosomes during meiosis I? What happens to chromosomes during meiosis II? Compare the sex cells produced by meiosis to the parent cell. Why is the difference between the sex cells and parent cell important? 6. Why are chromosomes important to heredity? 1. 2. 3. 4. 5. © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Section Summary The DNA Connection Key Concepts ■ What forms the genetic code? ■ How does a cell produce proteins? ■ How can mutations affect an organism? Today, scientists know that genes control the production of proteins in the cells of an organism. Proteins determine the size, shape, and other traits of organisms. Recall that chromosomes are composed mostly of DNA. A DNA molecule is made up of four nitrogen bases—adenine (A), thymine (T), guanine (G), and cytosine (C). The order of the nitrogen bases along a gene forms a genetic code that specifies what type of protein will be produced. In the genetic code, a group of three DNA bases codes for one specific amino acid. During protein synthesis, the cell uses information from a gene on a chromosome to produce a specific protein. Protein synthesis occurs on the ribosomes in the cytoplasm of the cell. DNA, however, is located in the cell nucleus. Before protein synthesis occurs, a genetic “messenger,” called ribonucleic acid or RNA, is made based on a code in the DNA. RNA is similar to DNA, except RNA has only one strand and it has uracil instead of thymine. In the first step of protein synthesis, the DNA molecule “unzips” and directs the production of messenger RNA. There are several types of RNA involved in protein synthesis. Messenger RNA copies the coded message from the DNA in the nucleus, and carries it to the ribosomes in the cytoplasm. Transfer RNA carries amino acids and adds them to the growing protein. Sometimes changes called mutations occur in a gene or chromosome. Mutations can cause a cell to produce an incorrect protein during protein synthesis. As a result, the organism’s trait, or phenotype, may be different from what it normally would have been. If a mutation occurs in a body cell, the mutation affects only the cell that carries it. However, if a mutation occurs in a sex cell, the mutation can be passed on to an offspring and affect the offspring’s phenotype. Some mutations are the result of small changes in an organism’s hereditary material. Others occur when chromosomes don’t separate correctly during meiosis. Some of the changes brought about by mutations are harmful to an organism. A few mutations, however, are helpful, and still others are neither harmful nor helpful. A mutation is harmful if it reduces an organism’s chance for survival and reproduction. Whether or not a mutation is harmful depends partly on the organism’s environment. For example, a white lemur may not survive in the wild, but the mutation has no effect on its ability to survive in a zoo. © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Guided Reading and Study The DNA Connection This section tells how the DNA molecule is related to genes, chromosomes, and the inheritance of traits. Use Target Reading Skills As you read, complete the flowchart below to show protein synthesis. Put the steps of the process in separate boxes in the flowchart in the order in which they occur. Protein Synthesis DNA provides code to form messenger RNA. Messenger RNA attaches to ribosome. The Genetic Code Circle the letter of each sentence that is true about genes, chromosomes, and proteins. a. Genes control the production of proteins in an organism’s cells. b. Proteins help determine the size, shape, and other traits of an organism. c. Chromosomes are made up mostly of proteins. d. A single gene on a chromosome contains only one pair of nitrogen bases. 2. What are the four nitrogen bases that make up a DNA molecule? ________________________________________________________________________ ________________________________________________________________________ © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Genetics: The Science of Heredity 1. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity The DNA Connection 3. ■ Guided Reading and Study (continued) What is the genetic code? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 4. One group of three nitrogen bases codes for one ________________________. How Cells Make Proteins 5. During protein synthesis, the cell uses information from a ________________________ on a chromosome to produce a specific ________________________. 6. Proteins are made on ________________________ in the cytoplasm of the cell. 7. Complete this Venn diagram to show some of the similarities and differences between DNA and RNA. Tell where each nucleic acid is located and what bases it contains. RNA DNA Stays inside the nucleus Adenine Guanine © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Guided Reading and Study 8. List the two kinds of RNA and describe their jobs. a. _____________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ b. _____________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 9. Circle the letter of the first step in protein synthesis. a. Transfer RNA carries amino acids to the ribosome. b. The ribosome releases the completed protein chain. c. Messenger RNA enters the cytoplasm and attaches to a ribosome. d. DNA “unzips” to direct the production of a strand of messenger RNA. 10. Circle the letter of the last step in protein synthesis. a. Transfer RNA carries amino acids to the ribosome. b. The protein chain grows longer as each transfer RNA molecule adds an amino acid. c. Messenger RNA enters the cytoplasm and attaches to a ribosome. d. DNA “unzips” to direct the production of a strand of messenger RNA. Mutations 11. What is a mutation? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 12. How can mutations affect protein synthesis in cells? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ Genetics: The Science of Heredity © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Guided Reading and Study The DNA Connection (continued) 13. Circle the letter of each sentence that is true about mutations. a. Cells with mutations will always make normal proteins. b. Some mutations occur when one nitrogen base is substituted for another. c. Some mutations occur when chromosomes don’t separate correctly during meiosis. d. Mutations that occur in a body cell can be passed on to an offspring. 14. Mutations can be a source of genetic ________________________. 15. Is the following sentence true or false? All mutations are harmful. ________________________ 16. Mutations that are ________________________ improve an organism’s chances for survival and reproduction. 17. Whether a mutation is harmful or helpful depends partly on an organism’s ________________________. © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Review and Reinforce The DNA Connection Understanding Main Ideas Complete the table below by stating whether each mutation is helpful, harmful, or neutral to the organism. Mutation Effect White lemur (in a zoo) 1. ________________________ White lemur (in the wild) 2. ________________________ Antibiotic resistance in bacteria 3. ________________________ Answer the following questions on the lines provided. 4. Describe what occurs during protein synthesis. _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ 5. What is the genetic code? _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ Building Vocabulary Fill in the blank to complete each statement. © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Genetics: The Science of Heredity 6. A ________________________ is any change in a gene or chromosome. 7. A type of RNA that carries amino acids and adds them to the growing protein is called ________________________ . 8. ________________________ is RNA that copies the coded message from the DNA in the nucleus and carries the message into the cytoplasm. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Enrich The Genetic Code The genetic code is made up of groups of three nitrogen bases in the messenger RNA. Each three-base group, called a codon, codes for one amino acid. The table below shows the genetic code. To find the amino acid that is coded for by the codon UGG in messenger RNA, look in the row of the first base in the codon—U. Then move to the box that is specified by the second base in the codon—G. Finally, look down the list of amino acids in the box until you find the one in row “G,” the third base in the codon. You should find that UGG is the codon for tryptophan. Transfer RNA matches up with the messenger RNA at the ribosome to deliver the correct amino acid to the growing protein chain. Transfer RNA has a three-base code called an anticodon that matches up with the codon in the messenger RNA. Answer the following questions on a separate sheet of paper. © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Third Base in Codon First Base in Codon The Genetic Code (messenger RNA) 1. If the DNA sequence of Lysine Arginine Isoleucine Threonine A a gene was Lysine Arginine Methionine Threonine G TACTTACCGAGC Serine Isoleucine Threonine A Asparagine U Asparagine Serine Isoleucine Threonine TAGACT, then C what is the sequence of the Glutamic acid Glycine Valine Alanine A messenger RNA? Glutamic acid Glycine Valine Alanine G Valine Alanine G Aspartic acid Glycine 2. Use the genetic U Aspartic acid Glycine Valine Alanine code to identify C the sequence of "Stop" codon "Stop" codon Leucine Serine amino acids A "Stop" codon Tryptophan Leucine Serine encoded by the G Cysteine Phenylanaline Serine U Tyrosine U messenger RNA Tyrosine Cysteine Phenylanaline Serine C that you identified in Question 1. Glutamine Arginine Leucine Proline A 3. What are the Glutamine Arginine Leucine Proline G sequences of the Arginine Leucine Proline C Histidine U Histidine Arginine Leucine Proline anticodons for the C transfer RNA G A U C molecules that carry each of the Second Base in Codon amino acids in the protein sequence that you identified in Question 2? 4. How would the protein change if a mutation caused a base to be added, making the mutated DNA sequence TACGTTACCGAGCTAGACT? How is the protein affected by this mutation? (Hint: How does the extra letter change the series of bases?) 5. How would the protein change if a mutation caused one base to replace another, making the mutated DNA sequence TACTTACCTAGCTAGACT? How does this mutation affect protein function? Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Key Terms Key Terms Use the clues below to identify Key Terms from the chapter. Write the terms below, putting one letter in each blank. When you finish, the word enclosed in the diagonal lines will reveal what Mendel studied. Clues 6. Number that describes the likelihood 1. The process by which the number of that a certain event will occur chromosomes is reduced by half in sex cells 7. An allele whose trait always shows up in the organism when the allele 2. A chart that shows all possible allele is present combinations resulting from a genetic cross 8. Physical characteristic of an organism 3. An organism’s physical appearance 9. A factor that controls a trait 4. RNA that copies the coded message 10. The scientific study of heredity in DNA 11. Offspring of many generations that 5. Describes an organism that has two have the same trait different alleles for a trait 1. ___ ___ ___ ___ ___ ___ ___ 2. ___ ___ ___ ___ ___ ___ ___ 3. 4. 5. ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ 6. ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ 7. ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ 9. ___ ___ ___ ___ 10. 11. ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Genetics: The Science of Heredity 8. Name ____________________________ Date ____________________ Class ____________ Connecting Concepts ■ Genetics: The Science of Heredity Connecting Concepts Develop a concept map that uses the Key Concepts and Key Terms from this chapter. Keep in mind the big ideas of this chapter. The concept map shown is one way to organize how the information in this chapter is related. You may use an extra sheet of paper. is the scientific study of which is the passing of traits from parent to offspring was revolutionized by Mendel who experimented with by setting up crosses between plants that are hybrid which have which have the same two different alleles for a trait Genetics is related to the math principle of which can be used to predict inheritance of traits using a Punnett square which shows all the possible combinations of that can result from a genetic cross is determined by the coding in the DNA which is copied by messenger RNA which is read by which links to make proteins © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Genetics: The Science of Heredity Laboratory Investigation TEACHER NOTES Chromosomes and Inheritance Key Concept Teaching Tips The traits of offspring are determined by the alleles of the parents. ■ Skills Focus observing, making models ■ Time 40 minutes Materials (per group) marker craft stick Alternate Materials: If craft sticks are unavailable, strips of cardboard or acetate could be used. Using clear, colorless acetate strips for recessive alleles and colored strips for dominant alleles can be helpful. ■ (Step 2) Remind students that scientists generally represent a dominant allele with a capital letter, often the initial of the word that best describes the trait, and the recessive allele with the corresponding lowercase letter. (More to Explore) Remind students that Punnett square results show only probabilities. The traits of offspring from actual matings may not match the predictions. (More to Explore) Based on the principles of probability, two of four, or 50%, of the young unimonsters would have curly hair (Cc), and two of four, or 50%, of the young unimonsters would have straight hair (cc). Advance Preparation Get enough craft sticks so that you have four for each group of students (eight if students do the More to Explore). Genetics: The Science of Heredity © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Laboratory Investigation Chromosomes and Inheritance Pre-Lab Discussion How are traits inherited? You can investigate this question by considering an imaginary animal called the unimonster. Suppose this animal has only one pair of chromosomes. Chromosomes carry genes, which control different genetic traits, such as hair color, height, and other physical characteristics. Different forms of a gene are called alleles. The presence of different alleles on the chromosomes of unimonsters determines whether they have one horn or two horns. During reproduction, parent unimonsters pass on alleles to their offspring. In this investigation, you will determine the different allele combinations for the offspring of two unimonsters and figure out the number of horns the young unimonsters will have. 1. What are dominant and recessive alleles? ________________________________________________________________________ ________________________________________________________________________ 2. Define genotype and phenotype. ________________________________________________________________________ ________________________________________________________________________ 3. What does it mean to say that an organism is homozygous for a trait? Heterozygous for a trait? ________________________________________________________________________ ________________________________________________________________________ 4. How do the numbers of chromosomes in cells compare with the number of chromosomes in sex cells? During reproduction, what fraction of chromosomes does each parent contribute to its offspring? ________________________________________________________________________ ________________________________________________________________________ Problem How can you determine the traits of a unimonster ’s offspring? Materials (per group) marker craft sticks © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Laboratory Investigation Procedure 1. Figure 1 shows a mother and a father unimonster, each with different genetic traits. The allele for two horns is dominant over the allele for one horn. Look at the drawing and answer question 1 in Observations. 2. The mother unimonster is heterozygous. This means that she has one allele for two horns and one allele for one horn. Each Mother Unimonster Father Unimonster of her sex cells will have either a Figure 1 chromosome with the two-horn allele or a chromosome with the one-horn allele. Follow Figure 2 and steps 3 and 4 to make a model of the mother unimonster ’s sex chromosomes. 3. One of the mother unimonster ’s chromosomes will carry the two-horn allele. Write "M1" (for mother) at one end of a craft stick. At the other end of the stick, write H for the dominant two-horn allele. 4. The mother unimonster ’s other chromosome will carry the one-horn allele. Write "M2" at the end of a second stick. At the other end, write h for the recessive one-horn allele. Figure 2 5. The father unimonster is homozygous (hh). Follow Figure 2 to make models of the father ’s chromosomes: F1 and F2. 6. During reproduction, the sex cells produced by the mother and father unimonsters combine to form a fertilized egg. The fertilized egg will grow into a young unimonster. Whether the young unimonster has one or two horns depends on the alleles on the chromosome contributed by each parent during reproduction. In Observations, use your chromosome models to answer questions 2–5. Remember that the allele for two horns is dominant. Anytime the dominant allele (H) is present, the unimonster will have two horns. Genetics: The Science of Heredity © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Laboratory Investigation Chromosomes and Inheritance (continued) Observations 1. Which unimonster parent has the dominant allele for number of horns? How do you know? ________________________________________________________________________ ________________________________________________________________________ 2. During reproduction, the sex cells containing the chromosomes M1 and F1 combine to form a fertilized egg. a. Which alleles are on each of the chromosomes? ________________________________________________________________________ b. Will the young unimonster have one horn or two horns? Draw the appropriate number of horns on young unimonster 1 in Figure 3. 3. During reproduction, the sex cells containing the chromosomes M1 and F2 combine to form a fertilized egg. a. Which alleles are on each of the chromosomes? ________________________________________________________________________ b. Will the young unimonster have one horn or two horns? Draw the appropriate number of horns on young unimonster 2 in Figure 3. 4. During reproduction, the sex cells containing the chromosomes M2 and F1 combine to form a fertilized egg. a. Which alleles are on each of the chromosomes? ________________________________________________________________________ b. Will the young unimonster have one horn or two horns? Draw the appropriate number of horns on young unimonster 3 in Figure 3. 5. During reproduction, the sex cells containing the chromosomes M2 and F2 combine to form a fertilized egg. a. Which alleles are on each of the chromosomes? ________________________________________________________________________ b. Will the young unimonster have one horn or two horns? Draw the appropriate number of horns on young unimonster 4 in Figure 3. Young Unimonster 1 Young Unimonster 2 Young Unimonster 3 Young Unimonster 4 Figure 3 © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Name ____________________________ Date ____________________ Class ____________ Genetics: The Science of Heredity ■ Laboratory Investigation Analyze and Conclude 1. Which young unimonster(s) are homozygous and have one horn? ________________________________________________________________________ ________________________________________________________________________ 2. Which young unimonster(s) are heterozygous? ________________________________________________________________________ ________________________________________________________________________ 3. Are any young unimonster(s) homozygous with two horns? Explain. ________________________________________________________________________ ________________________________________________________________________ Critical Thinking and Applications 1. If a mother unimonster is homozygous and has two horns, and a father unimonster is homozygous and has one horn, what are the phenotypes and genotypes of the possible offspring? Remember that the two-horn allele is dominant. ________________________________________________________________________ ________________________________________________________________________ 2. Predict the phenotypes and genotypes of the offspring of a mother unimonster and a father unimonster that are both heterozygous. ________________________________________________________________________ ________________________________________________________________________ More to Explore Repeat the lab for the traits of curly hair versus straight hair. Assume that the curly-hair allele is dominant and the straight-hair allele is recessive. The mother is homozygous and has straight hair, while the father is heterozygous. Get four more craft sticks. Make all the combinations of different alleles. Determine all of the possible genotypes and the resulting phenotypes of the offspring. You may wish to use the Punnett square below to record the genotypes. C c c c © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. Genetics: The Science of Heredity Mother’s Alleles for Curly Hair Father’s Alleles for Curly Hair