Chapter 13: Meiosis and Sexual Life Cycles

Transcription

1 Name Period Concept 13.1 Offspring acquire genes from parents by inheriting chromosomes 1. Let s begin with a review of several terms that you may already know. Define: gene locus gamete male gamete female gamete asexual reproduction sexual reproduction 2. How many chromosomes are in human cells? What is a chromosome? 3. Which type of reproduction will result in genetically identical offspring? Concept 13.2 Fertilization and meiosis alternate in sexual life cycles 4. What is a somatic cell? Give examples of two human somatic cell types. 5. How does a somatic cell compare to a gamete in terms of chromosome number? Copyright 2010 Pearson Education, Inc. -1-

2 6. Distinguish between sex chromosomes and autosomes. How many of each are found in human cells? Explanation # in Human Cells Sex chromosome Autosome 7. What is a karyotype? How is it prepared? What are three things that can be determined from a karyotype? 8. Explain what is meant by homologous chromosomes. 9. Cells that have only one of each homologous pair are said to be haploid, a condition that is represented by n. Cells that have two of each homologous pair are said to be diploid or 2n. For each of the following, is the cell haploid or diploid? liver cell gamete egg zygote skin cell sperm somatic cell sex cell 10. The muscle cells of a dog have 78 chromosomes. Fill in the correct chromosome number in a: bone cell sperm haploid cell somatic cell zygote Copyright 2010 Pearson Education, Inc. -2-

3 11. In the cell at right, the chromosomes are shaded in two colors to represent the parent of origin. On this sketch, label the following: a. sister chromatids b. homologous chromosomes c. centromere d. replicated chromosome e. maternal chromosomes 12. How many chromosomes does the cell above have? How many homologous pairs? How many chromatids? Is this cell haploid or diploid? 13. Where are the gametes of an animal produced? Be specific as to male and female gametes. 14. By what process are gametes produced? 15. What is another term for a fertilized egg? What is the chromosome number of the fertilized egg? (Answer this in general terms, haploid, n, or diploid, 2n.) 16. What is the purpose of meiosis? 17. Study Figure You will see that plants have a life cycle that involves spores, which form as a result of meiosis, so these spores are haploid. Notice also that both haploid and diploid cells can divide by mitosis. However, meiosis always begins with cells that are, and as a result of meiosis, daughter cells are formed that are always. These cells can be gametes (in animals) or spores (in plants). Copyright 2010 Pearson Education, Inc. -3-

4 18. Your study of plants this year will include knowing that they exhibit alternation of generations. What does this mean? What are the two generations? Which is haploid, and which is diploid? Use this information to label the moss life cycle here. Concept 13.3 Meiosis reduces the number of chromosome sets from diploid to haploid 19. What are alleles? Give an example. 20. In meiosis, the DNA is replicated during interphase, followed by two divisions. The first division is meiosis I. Study the events of prophase I as they are significant. Explain each of these events: synapsis crossing over PROPHASE I chiasmata 21. The figure at the right shows metaphase I. How is the arrangement of chromosomes different from metaphase of mitosis? METAPHASE I Copyright 2010 Pearson Education, Inc. -4-

5 22. There will be two divisions in meiosis. What will separate in the first division in meiosis I? 23. Now study the chromosomes in anaphase I and telophase I carefully. How many chromosomes are in each cell at the end of the first meiotic division? Are the resultant daughter cells haploid, or diploid? ANAPHASE I TELOPHASE I 24. From this figure, you should see that chromosome number is reduced in meiosis I and that the daughter cells at the end of meiosis I are haploid. Remember this! 25. During meiosis I, homologous chromosomes separate. What separates during meiosis II? 26. To check that you have the big picture, here are some quick review questions. a. What happens to chromosome number in meiosis? b. During which division is the chromosome number reduced? c. What is the purpose of meiosis? d. How many times does the cell divide in meiosis? e. How many times do the chromosomes duplicate? f. How many daughter cells are formed? g. What is the chromosome number? Copyright 2010 Pearson Education, Inc. -5-

6 h. What are homologs (homologous chromosomes)? i. What occurs in synapsis? j. What is crossing over? 27. Use Figure 13.9 to compare of mitosis and meiosis. Add these labels: Parent cell, Mitosis, Meiosis, Synapsis, Homologous chromosomes, Replicated chromosomes, Sister chromatids, Daughter cells, Meiosis I, Meiosis II, Crossing over As you label the drawing, carefully think about each process and review its important features. Copyright 2010 Pearson Education, Inc. -6-

7 28. Students often get confused about the differences between mitosis and meiosis. To help with this, work through the following chart: Role in the animal body Number of DNA replications Number of divisions Number of daughter cells Chromosome number of daughter cells Mitosis Meiosis 29. Synapsis and crossing over are unique to meiosis. During what specific phase do these occur? 30. Explain the physical events of crossing over. You may wish to make a sketch of the event. Include these terms: synaptonemal complex, chiasmata, homologs, sister chromatids. Concept 13.4 Genetic variation produced in sexual life cycles contributes to evolution 31. An important idea for you to understand is that new alleles arise by changes in the DNA or mutation, but genetic diversity occurs when the deck that is dealt is simply reshuffled. So, there are three ways that sexually reproducing organisms shuffle the deck. They are listed below. Explain what occurs in each, and how this increases diversity. independent assortment of chromosomes crossing over random fertilization Copyright 2010 Pearson Education, Inc. -7-

8 32. Here is a fun exercise to drive this point home. Pull out your calculator, and try your hand at this: When you were conceived, what were the odds that of the many possibilities, your parents would come up with you? a. The number of different gametes that can be formed because of independent assortment is 2n, where n = the number of homologous pairs Therefore, since humans have 46 chromosomes or 23 homologous pairs, what is the number of possible gametes that can be formed due to independent assortment of chromosomes? b. Now, this is the number of unique gametes your mom could have made. Your father could have made the same number. To see the effect of random fertilization, multiply the number of gametes one parent could make by the number of unique gametes the other parent could make. Your answer should be in the trillions, and all of this is without crossing over. See how special you are? Copyright 2010 Pearson Education, Inc. -8-

9 Testing Your Knowledge: Self-Quiz Answers Now you should be ready to test your knowledge. Place your answers here: Follow the directions for Self-Quiz question 10, DRAW IT by labeling the appropriate structures with these terms, drawing lines or brackets as needed: chromosome (label as replicated or unreplicated), centromere, kinetochore, sister chromatids, nonsister chromatids, homologous pair, homologs, chiasma, sister chromatid cohesion, and then answer questions 8 and Copyright 2010 Pearson Education, Inc. -9-

10 Chapter14: Mendel and the Gene Idea Chapter 14: Mendel and the Gene Idea Name Period If you have completed a first-year high school biology course, some of this chapter will serve as a review for the basic concepts of Mendelian genetics. For other students, this may be your first exposure to genetics. In either case, this is a chapter that should be carefully mastered. Spending some time with this chapter, especially working genetics problems, will give you a solid foundation for the extensive genetics unit in the chapters to come. Overview: 1. In the 1800s the most widely favored explanation of genetics was blending. Explain the concept of blending, and then describe how Mendel s particulate (gene) theory was different. Concept 14.1 Mendel used the scientific approach to identify two laws of inheritance 2. One of the keys to success for Mendel was using pea plants. Explain how using pea plants allowed Mendel to control mating; that is, how did this approach let Mendel be positive about the exact characteristics of each parent? 3. Define the following terms. Then, consider your own family. Which generation would your Mom s grandparents be? Your Mom? You? P generation F 1 generation F 2 generation Copyright 2010 Pearson Education, Inc

11 Chapter14: Mendel and the Gene Idea 4. Explain how Mendel s simple cross of purple and white flowers did the following: refuted blending determined dominant and recessive characteristics demonstrated the merit of experiments that covered multiple generations 5. Alternate versions of the same gene, like purple and white flower color, are termed. 6. On the figure at below, label the allele for both purple and white flower color, a homologous pair, and the locus of the flower color gene. 7. In sexually reproducing organisms, why are there exactly two chromosomes in each homologue? 8. Mendel s model consists of four concepts. Describe each concept in the appropriate space below. Indicate which of the concepts can be observed during meiosis by placing an asterisk by the concept. Mendel s Four Concepts Description of Concept 1st concept 2nd concept 3rd concept 4th concept (law of segregation) Copyright 2010 Pearson Education, Inc

12 Chapter14: Mendel and the Gene Idea 9. Using Figure 14.5 as your guide, provide the missing notations for the figure below. (P, F 1, F 2 ). a. What is the F 2 phenotypic and genotypic ratio? b. Which generation is completely heterozygous? c. Which generation has both heterozygous and homozygous offspring? 10. In pea plants, T is the allele for tall plants, while t is the allele for dwarf plants. If you have a tall plant, demonstrate with a test cross how it could be determined if the plant is homozygous tall or heterozygous tall. 11. Explain the difference between a monohybrid cross and a dihybrid cross. Copyright 2010 Pearson Education, Inc

13 Chapter14: Mendel and the Gene Idea 12. As you start to work word problems in genetics, two things are critical: the parent s genotype must be correct, and the gametes must be formed correctly. Using Figure 14.8 as your guide, explain how the gametes are derived for the following cross. (You should have four different gametes). YyRr YyRr 13. Complete the cross given in questions 12 by placing the gametes in a Punnett square. Then provide the phenotypic ratio of the offspring. Phenotypes/Phenotypic Ratio 14. Explain Mendel s law of independent assortment. Before leaving this concept, it would be helpful to complete the three problems in the 14.1 Concept Check on page 269 of your textbook. The problems are worked and explained in the Answer section on page A-10 at the back of the book. Concept 14.2 The laws of probability govern Mendelian inheritance 15. An event that is certain to occur has a probability of, while an event that is certain not to occur has a probability of. 16. In probability, what is an independent event? 17. State the multiplication rule and give an original example. 18. State the addition rule and give an original example. Copyright 2010 Pearson Education, Inc

14 Chapter14: Mendel and the Gene Idea 19. What is the probability that a couple will have a girl, a boy, a girl, and a boy in this specific order? Concept 14.3 Inheritance patterns are often more complex than those predicted by simple Mendelian genetics 20. Explain how incomplete dominance is different from complete dominance, and give an example of incomplete dominance. 21. Compare and contrast codominance with incomplete dominance. 22. Dominant alleles are not necessarily more common than recessive alleles in the gene pool. Explain why this is true. 23. Explain what is meant when a gene is said to have multiple alleles. 24. Blood groups are so important medically that you should be able to solve genetics problems based on blood types. The first step in accomplishing that is to understand the genotypes of each blood type. Before working any problems, complete this ABO blood type chart. Genotype Red Blood Cell Appearance Phenotype (blood group) Copyright 2010 Pearson Education, Inc

15 Chapter14: Mendel and the Gene Idea 25. Question 2 in the 14.3 Concept Check is a blood type problem. Complete it here, and show your work. 26. What is pleiotropy? Explain why this is important in diseases like cystic fibrosis and sicklecell disease. 27. Explain epistasis. 28. Explain why the dihybrid cross detailed in Figure has 4 white mice instead of the 3 that would have been predicted by Mendel s work. 29. Why is height a good example of polygenic inheritance? 30. Quantitative variation usually indicates. 31. Using the terms norm of reaction and multifactorial, explain the potential influence of the environment on phenotypic expression. Copyright 2010 Pearson Education, Inc

16 Chapter14: Mendel and the Gene Idea Concept 14.4 Many human traits follow Mendelian patterns of inheritance 32. Pedigree analysis is often used to determine the mode of inheritance (dominant or recessive, for example). Be sure to read the Tips for pedigree analysis in Figure 14.15; then complete the unlabeled pedigree by indicating the genotypes for all involved. What is the mode of inheritance for this pedigree? 33. Explain why you know the genotype of one female in the third generation, but are unsure of the other. 34. Describe what you think is important to know medically about the behavior of recessive alleles. 35. Students are expected to have a general knowledge of the pattern of inheritance and the common symptoms of a number of genetic disorders. Provide this information for the disorders listed below. a. cystic fibrosis b. sickle-cell disease Copyright 2010 Pearson Education, Inc

17 Chapter14: Mendel and the Gene Idea c. achondroplasia d. Huntington s disease 36. Amniocentesis and chorionic villus sampling are the two most widely used methods for testing a fetus for genetic disorders. Use the unlabeled diagram below to explain the three main steps in amniocentesis and the two main steps of CVS. 37. What are the strengths and weaknesses of each fetal test? 38. Explain the symptoms of phenylketonuria, and describe how newborn screening is used to identify children with this disorder. Copyright 2010 Pearson Education, Inc

18 Chapter14: Mendel and the Gene Idea Testing Your Knowledge: Genetics Problems (pg. 284) Now you should be ready to test your knowledge. This chapter does not have a Self-Quiz, but rather asks you to do a series of problems. One of the ways to determine your understanding of Mendelian genetics is to work many genetic problems. Complete the questions from the problems at the end of the chapter. Before starting, it would be productive to read the Tips for Genetic Problems on page 283. Work neatly, and show all work. As you know, you can check your solutions in your text. Questions 1, 2, 3, 5, 6, 7, 8, 9, 13, 16, 17, 19 Copyright 2010 Pearson Education, Inc