Solution Manual for Concepts of Genetics 4th Edition By Robert Brooker

Solution Manual for Concepts of Genetics 4th Edition By RobertBrooker Page | 2 Copyright 2022 © McGraw Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. CONCEPTS OF GENETICS, 4/e ANSWERS TO PROBLEM SETS Chapters 1-24 CHAPTER 1 Note: the answers to the Comprehension Questions are at the end of the chapter. Concept Check Questions (in figure legends) FIGURE 1. 1 Understanding our genes may help with diagnoses of inherited diseases. It may also lead to the development of drugs to combat diseases. Other answers are possible. FIGURE 1. 2 Many ethical issues are associated with human cloning. Is it the wrong thing to do? Does it conflict an individual’s religious views? And so on. FIGURE 1. 3 Because females mate only once, sorting out the male mosquitoes and releasing sterile males into the environment can limit mosquito reproduction. FIGURE 1. 4 DNA is a macromolecule. FIGURE 1. 5 DNA and proteins are found in chromosomes. A small amount of RNA may also be associated with chromosomes when transcription is occurring, and as discussed in Chapter 18, some non-coding RNAs may bind to chromosomes. FIGURE 1.6 The information to make a polypeptide is stored in DNA. FIGURE 1. 7 The dark-colored butterfly has a more active pigment-producing enzyme. FIGURE 1. 8 Genetic variation is the reason the frogs look different. FIGURE 1. 9 These are examples of variation in chromosome number. FIGURE 1. 10 If this girl had been given a standard diet, she would have developed the harmful symptoms of PKU, which include mental impairment and foul-smelling urine. FIGURE 1. 11 Page | 3 Copyright 2022 © McGraw Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. A corn gamete contains 10 chromosomes. (The leaf cells are diploid.) FIGURE 1. 12 The horse populations have become adapted to their environment, which has changed over the course of many years. FIGURE 1.13 There are several possible examples of other model organisms, including rats and frogs. End-of-chapter Questions: Conceptual Questions C1. A chromosome is a very long polymer of DNA. A gene is a specific sequence of DNA within that polymer; the sequence of bases creates a gene and distinguishes it from other genes. Genes are located in chromosomes, which are found within living cells. C2. At the molecular level, a gene (a sequence of DNA) is first transcribed into RNA. The genetic code within the RNA is used to synthesize a protein with a particular amino acid sequence. This second process is called translation. C3. A. Molecular level. This is a description of a how an allele affects protein function. B. Cellular level. This is a description of how protein function affects cell structure. C. Population level. This is a description of how the two alleles affect members of a population. D. Organism level. This is a description of how the alleles affect the traits of an individual. C4. Genetic variation is the occurrence of genetic differences within members of the same species or different species. Within any population, variation may occur in the genetic material. Variation may occur in particular genes, so some individuals carry one allele and other individuals carry a different allele. Examples include differences in coat color among mammals or flower color in plants. At the molecular level, this type of genetic variation is caused by changes in the DNA sequences of genes. There may also be variation in chromosome structure and number. C5. An extra chromosome (specifically an extra copy of chromosome 21) causes Down syndrome. C6. You can pick almost any trait. For example, flower color in petunias would be an interesting choice. Some petunias are red and others are purple. There must be different alleles in a flower color gene that affect this trait in petunias. In addition, the amount of sunlight, fertilizer, and water also affects the intensity of flower color. C7. The term diploid means that a cell has two copies of each type of chromosome. In humans, nearly all of the cells are diploid except for gametes (i.e., sperm and egg cells). Gametes usually have only one set of chromosomes. C8. A DNA sequence is a sequence of nucleotides. Each nucleotide may have one of four different bases (i.e., A, T, G, or C). When speaking of a DNA sequence, the focus is on the sequence of those bases. C9. The genetic code is the way in which the sequence of bases in RNA is read to produce a sequence of amino acids within a protein. C10. A. A gene is a segment of DNA. For most genes, the expression of the gene results in the production of a polypeptide, which is a unit of a protein. The functioning of proteins within living cells largely determines the traits of an organism. Page | 4 Copyright 2022 © McGraw Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. B. A gene is a segment of DNA that usually encodes the information for the production of a specific polypeptide. Genes are found within chromosomes. Many genes are found within a single chromosome. C. An allele is an alternative version of a particular gene. For example, suppose a plant has a flower color gene. One allele could produce a white flower, while a different allele could produce an orange flower. The white allele and orange allele are alleles of the flower color gene. D. A DNA sequence is a sequence of bases, which are found within nucleotides. The information within a DNA sequence (which is transcribed into an RNA sequence) specifies the amino acid sequence within a polypeptide. C11. The statement in part A is not correct. Individuals do not evolve. Populations evolve because certain individuals are more likely to survive and reproduce and pass their genes to succeeding generations. C12. A. How genes and traits are transmitted from parents to offspring. B. How the genetic material functions at the molecular and cellular levels. C. Why genetic variation exists in populations, and how it changes over the course of many generations. Application and Experimental Questions E1. There are many possible answers. Some common areas to discuss might involve the impact of genetics in the production of new medicines, the diagnosis of diseases, the production of new kinds of food, and the use of DNA fingerprinting to solve crimes. E2. A genetic cross involves breeding two different individuals. E3. This would be used to a great extent by molecular geneticists. The sequence of DNA is a molecular characteristic of DNA. In addition, the sequence of DNA is interesting to transmission and population geneticists as well. E4. You would see 47 chromosomes instead of 46. There would be three copies of chromosome 21 instead of two copies. E5. A. Transmission geneticists. Dog breeders are interested in how genetic crosses affect the traits of dogs. B. Molecular geneticists. This is a good model organism to study genetics at the molecular level. C. Both transmission geneticists and molecular geneticists. Fruit flies are easy to cross and study the transmission of genes and traits from parents to offspring. Molecular geneticists have also studied many genes in fruit flies to see how they function at the molecular level. D. Population geneticists. Most wild animals and plants would be the subject of population geneticists. In the wild, you cannot make controlled crosses. But you can study genetic variation within populations and try to understand its relationship to the environment. E. Transmission geneticists. Agricultural breeders are interested in how genetic crosses affect the outcome of traits. E6. You need to follow the scientific method. You can take a look at an experiment in another chapter to see how the scientific method is followed. Page | 5 Copyright 2022 © McGraw Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. CHAPTER 2 Note: the answers to Comprehension Questions are at the end of the chapter. Concept Check Questions (in figure legends) FIGURE 2. 1 Compartmentalization means that cells have membrane-bound compartments. FIGURE 2. 2 The chromosomes would not be spread out very well, and would probably be overlapping. It would be difficult to see individual chromosomes. FIGURE 2. 3 Homologs are similar in size, banding pattern, and carry the same types of genes. However, the alleles of a given gene may be different. FIGURE 2. 4 FtsZ assembles into a ring at the future site of the septum and recruits to that site other proteins that produce a cell wall between the two daughter cells. FIGURE 2. 5 In the G1 phase of the cell cycle, a cell may be preparing to divide. By comparison, the G0 phase is a phase in which a cell is either not advancing through the cell cycle or has committed to never divide again. FIGURE 2. 6 Homologs are genetically similar; one is inherited from the mother and the other from the father. By comparison, chromatids are the product of DNA replication. The chromatids within a pair of sister chromatids are genetically identical. FIGURE 2.7 One end of a kinetochore microtubule is attached to a kinetochore on a chromosome. The other end is within the centrosome. FIGURE 2. 8 Anaphase FIGURE 2. 9 Ingression occurs because myosin motor proteins shorten the contractile ring, which is formed from actin proteins. FIGURE 2. 10 The end result of crossing over is that homologous chromosomes have exchanged pieces. FIGURE 2. 11 The cells at the end of meiosis are haploid, whereas the mother cell is diploid. FIGURE 2. 12 In metaphase of mitosis, each pair of sister chromatids is attached to both poles, whereas in metaphase of meiosis I, each pair of sister chromatids is attached to just one pole. FIGURE 2. 13 Polar bodies are small cells that are produced during oogenesis and then degenerate. FIGURE 2. 14 All of the nuclei in the embryo sac are haploid. The central cell has two haploid nuclei, and all of the other cells, including the egg, have just one. Page | 6 Copyright 2022 © McGraw Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. End-of-chapter Questions: Conceptual Questions C1. They are genetically identical, barring rare mutations, because they receive identical copies of the genetic material from the mother cell. C2. A homolog is one of the members of a chromosome pair. Homologs are usually the same size and carry the same types and order of genes. They may differ in that the genes they carry may be different alleles. C3. Sister chromatids are identical copies derived from the replication of a chromosome. They remain attached to each other at the centromere. They are genetically identical, barring rare mutations and crossing over with homologous chromosomes. C4. Metaphase is the organization phase, and anaphase is the separation phase. C5. G1, there should be six linear chromosomes. In G2, there should be 12 chromatids that are attached to each other in pairs of sister chromatids. C6. In metaphase of meiosis I, each pair of chromatids is attached to only one pole via the kinetochore microtubules. In metaphase of mitosis, there are two attachments (i.e., to both poles). If the attachment is lost, a chromosome will not migrate to a pole and may not become enclosed in a nuclear membrane after telophase. If left out in the cytosol, it would eventually be degraded. C7. A. During mitosis and meiosis II B. During meiosis I C. During mitosis, meiosis I, and meiosis II D. During mitosis and meiosis II C8. The reduction occurs because there is a single DNA replication event but two cell divisions. Because of the nature of separation during anaphase of meiosis I, each cell receives one copy of each type of chromosome. C9. C10. It means that the maternally derived and paternally derived chromosomes are randomly aligned along the metaphase plate during metaphase of meiosis I. Page | 7 Copyright 2022 © McGraw Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. C11. Mitosis—two diploid cells containing 10 chromosomes each (two complete sets). Meiosis—four haploid cells containing 5 chromosomes each (one complete set) C12. The number of different, random alignments equals 2n , where n equals the number of chromosomes per set. In this case, there are three per set, so the possible number of arrangements equals 2 3 , which is 8. C13. (1/2)n = (1/2)4 = 1/16 or 6.25% C14. The probability would be much lower because pieces of maternal chromosomes would be incorporated into the paternal chromosomes. Therefore, a gamete would be unlikely to carry a chromosome that was completely paternally derived. C15. Bacteria do not need to sort their chromosomes because they only have one type of chromosome. Though not discussed in the text, the attachment of the two copies of the chromosomes to the cell membrane prior to cell division also helps to ensure that each daughter cell receives one copy. C16. During interphase, the chromosomes are greatly extended. In this conformation, they might get tangled up with each other and not sort properly during meiosis and mitosis. The condensation process probably occurs so that the chromosomes easily align along the equatorial plate during metaphase without getting tangled up. C17. To produce identical quadruplets, fertilization begins with one sperm and one egg cell. This fertilized egg then could divide twice by mitosis to produce four genetically identical cells. These four cells could then separate from each other to begin the lives of four distinct individuals. Another possibility is that mitosis could produce two cells that separate from each other. These two cells could then divide by mitosis to produce two pairs of cells, which also could separate to produce four individual cells. C18. During prophase of meiosis II, your drawing should show four replicated chromosomes (i.e., four structures that look like Xs). Each chromosome is one homolog. During prophase of mitosis, there should be eight replicated chromosomes (i.e., eight Xs). During prophase of mitosis, there are pairs of homologs. The main difference is that prophase of meiosis II has a single copy of each of the four chromosomes, whereas prophase of mitosis has four pairs of homologs. At the end of meiosis I, each daughter cell has received only one copy of a homologous pair, not both. This is due to the alignment of homologs during metaphase of meiosis I and their separation during anaphase of meiosis I. C19. The products of meiosis have only one copy of each type of chromosome. For example, one human gamete may contain the paternally derived copy of chromosome 11, whereas a different gamete may contain the maternally derived copy of chromosome 11. These two homologs may carry different alleles of the same genes and therefore are not identical. In contrast, mitosis produces genetically identical daughter cells that have both copies of all the pairs of homologous chromosomes. C20. DNA replication does not take place during interphase II. The chromosomes at the end of telophase of meiosis I have already replicated (i.e., they are found in pairs of sister chromatids). During meiosis II, the sister chromatids separate from each other, yielding individual chromosomes. C21. Prophase/Prometaphase Telophase Nuclear membrane dissociates. Nuclear membrane re-forms. Mitotic spindle forms. Mitotic spindle disassembles. Page | 8 Copyright 2022 © McGraw Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Chromosomes condense. Chromosomes decondense. Chromosomes attach to spindle. Chromosomes detach from the spindle. C22. A. 20 B. 10 C. 30 D. 20 C23. The hybrid offspring would have 44 chromosomes (i.e., 25 + 19). The reason for infertility is because each chromosome does not have a homologous partner. Therefore, the chromosomes cannot properly pair during metaphase of meiosis I, and the gametes do not receive one copy of each homolog. Gametes will be missing certain chromosomes, which makes them infertile. C24. Male gametes are usually small and mobile. Animal and some plant male gametes have flagella, which make them motile. The mobility of the male gamete makes it likely that it will come in contact with the female gamete. Female gametes are usually much larger and contain nutrients to help the growth of the embryo after fertilization occurs. C25. To produce sperm, a spermatogonial cell first goes through mitosis to produce two cells. One of these remains a spermatogonial cell and the other advances through meiosis. In this way, the testes continue to maintain a population of spermatogonial cells. C26. During oogenesis in humans, the cells are arrested in prophase of meiosis I for many years until selected primary oocytes advance through the rest of meiosis I and begin meiosis II. If fertilization occurs, meiosis II is completed. C27. There is a 1/2 chance that the mother will transmit her abnormal chromosome and a 1/2 chance that the father will. You use the product rule to calculate the chances of both outcomes happening. So the answer is 1/2 × 1/2 = 1/4, or 25%. The probability that such a child will pass both chromosomes to an offspring is also 25% because that child had a 1/2 chance of passing either chromosome. Application and Experimental Questions E1. A. G2 phase (it could not complete prophase) B. Metaphase (it could not enter anaphase) C. Telophase (it could not divide into two daughter cells) D. G2 phase (it could not enter prophase) E2. During interphase, the chromosomes are longer, thinner, and much harder to see. In metaphase, they are highly condensed, which makes them thicker and shorter. E3. You could karyotype other members of the family and see if affected members always carry the abnormal chromosome. Questions for Student Discussion/Collaboration 1. It’s not possible to give a direct answer, but the point is for students to be able to draw chromosomes in different configurations and understand the various phases. The chromosomes may or may not be: 1. In homologous pairs 2. Connected as sister chromatids 3. Associated in bivalents 4. Lined up in metaphase Page | 9 Copyright 2022 © McGraw Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 5. Moving toward the poles. 2. A major advantage of sexual reproduction is that it fosters genetic diversity in future populations. A major disadvantage is that to reproduce, each individual must find a mate of the opposite sex. CHAPTER 3 Note: the answers to Comprehension Questions are at the end of the chapter. Concept Check Questions (in figure legends) FIGURE 3. 2 The male gamete is found within pollen. FIGURE 3. 3 The white flower is providing the sperm and the purple flower is providing the eggs. FIGURE 3. 4 A true-breeding strain maintains the same trait over the course of many generations. FIGURE 3. 6 Segregation means that the T and t alleles separate from each other so that a haploid cell receives one of them, but not both. FIGURE 3. 7 In this hypothesis, two different genes are linked. The alleles of the same gene are not linked. FIGURE 3. 9 Independent assortment allows for new combinations of alleles among different genes to be found in future generations of offspring. FIGURE 3. 10 Such a parent could make two types of gametes, Ty and ty, in equal proportions. FIGURE 3. 12 Homologous chromosomes separate at anaphase of meiosis I. FIGURE 3. 13 chromosomes could line up in four different ways. FIGURE 3. 14 Horizontal lines connect two individuals that have offspring together, and they connect all of the offspring that produced by the same two parents. End-of-chapter Questions: Conceptual Questions C1. Mendel’s work showed that genetic determinants are inherited in a dominant/recessive manner. This was readily apparent in many of his crosses. For example, when he crossed two true-breeding plants for a trait such as height (i.e., tall versus dwarf), all the F1 plants were tall. This is inconsistent with blending. Perhaps more striking was the result obtained in the F2 generation: 3/4 of the offspring were tall and 1/4 were short. In other words, the F2 generation displayed phenotypes that were like the parental generation. There did not appear to be a blending to create an intermediate phenotype. Instead, the genetic determinants did not seem to change from one generation to the next. Page | 10 Copyright 2022 © McGraw Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. C2. In plants, cross-fertilization occurs when the pollen and eggs come from different plants; in selffertilization they come from the same plant. C3. The genotype is the type of genes that an individual inherits while the phenotype is the individual’s observable traits. Tall pea plants, red hair in humans, and vestigial wings in fruit flies are phenotypes. Homozygous, TT, in pea plants; a heterozygous carrier of the cystic fibrosis allele; and homozygotes for the cystic fibrosis allele are descriptions of genotypes. It is possible to have different genotypes and the same phenotype. For example, a pea plant that is TT or Tt would both have a tall phenotype. C4. A true-breeding organism is homozygote that has two copies of the same allele. C5. Conduct a cross in which the unknown individual is mated to an individual that carries only recessive alleles for the gene in question. C6. Diploid organisms contain two copies of each type of gene. When they make gametes, only one copy of each gene is found in a gamete. Two alleles cannot stay together within the same gamete. C7. B. This statement is not correct because these are alleles of different genes. C8. Genotypes: 1 Tt : 1 tt Phenotypes: 1 tall : 1 dwarf C9. The recessive phenotype must be a homozygote. The dominant phenotype could be either homozygous or heterozygous. C10. In this cross, c is the recessive allele for constricted pods; Y is the dominant allele for yellow color. The cross is ccYy × CcYy. Follow the directions for setting up a Punnett square, as described in Section 3.3. The genotypic ratio is 2 CcYY : 4 CcYy : 2 Ccyy : 2 ccYY : 4 ccYy : 2 ccyy. This 2:4:2:2:4:2 ratio can be reduced to a 1:2:1:1:2:1 ratio. The phenotypic ratio is 6 smooth pods, yellow seeds : 2 smooth pods, green seeds: 6 constricted pods, yellow seeds : 2 constricted pods, green seeds. This 6:2:6:2 ratio could be reduced to a 3:1:3:1 ratio. C11. The genotypes are 1 YY : 2 Yy : 1 yy. The phenotypes are 3 yellow : 1 green. C12. Offspring with a nonparental phenotype are consistent with the idea of independent assortment. If two different traits were always transmitted together as unit, it would not be possible to get nonparental phenotypic combinations. For example, if a true-breeding parent had two dominant traits and was crossed to a true-breeding parent having the two recessive traits, the F2 generation could not have offspring with one recessive and one dominant trait. However, because independent assortment can occur, it is possible for F2 offspring to have one dominant and one recessive trait. C13. (a) It behaves like a recessive trait because unaffected parents sometimes produce affected offspring. In such cases, the unaffected parents are heterozygous carriers. (b) It behaves like a dominant trait. An affected offspring always has an affected parent. However, recessive inheritance cannot be ruled out. C14. A. Barring a new mutation during gamete formation, the probability is 100%. They must be heterozygotes in order to produce a child with a recessive disorder. B. Construct a Punnett square. There is a 50% chance of heterozygous offspring. C. Use the product rule. The chance of being phenotypically unaffected is 0.75 (i.e., 75%), so the answer is 0.75 × 0.75 × 0.75 = 0.422, which is 42.2%. D. Use the binomial expansion equation, where n = 3, x = 2, p = 0.75, q = 0.25. The answer is 0.422, or 42.2%. Page | 11