Chapter 4: Mutation and Genetic Variation

1.	What is the difference between a silent site mutation and a replacement mutation? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
2.	How do chromosome inversions occur? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
3.	Diagram the sequence of events that leads to the formation of second-generation polyploid individuals in plants that can self-fertilize. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
4.	How does unequal cross-over lead to the duplication of DNA sequences? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
5.	According to the data available to date, are most mutations deleterious, beneficial, or neutral? On average, are their fitness effects large, small, or nonexistent? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
6.	What is a transition? What is a transversion? Which is more common? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
7.	Why are the terms "point mutation" and "gene duplication" appropriate? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
8.	Why is genetic variation important in evolution? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
9.	Discuss why mutation rates vary among individuals within populations, and among species. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
10.	Compare and contrast the evolutionary effects of point mutations, chromosome inversions, gene duplications, and polyploidization. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
11.	Mutation rates can be estimated by indirect methods, which usually rely on observations of phenotypes caused by loss-of-function mutations, or by direct methods, which compare DNA sequences before and after mutations have been allowed to accumulate over time. What are the pros and cons of each approach? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
12.	What are the possible fates of a gene sequence that becomes duplicated due to unequal crossing-over? What events lead to each of these consequences? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
13.	What evidence do researchers use to defend the hypothesis that two or multiple stretches of DNA sequence are related by gene duplication events? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
14.	Compare and contrast the most popular methods for assessing the amount of genetic variation present in populations. How much of the actual variation present do these methods reveal? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
15.	Suppose a silent site mutation occurs in an exon that is part of the gene in a human. Has a new allele been created? Defend your answer. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
16.	The amino acid sequences encoded by the red and green visual pigment genes found in humans are 96% identical (Nathans et al. 1986). These two loci are found close together on the X chromosome, while the locus for the blue pigment is located on chromosome 7. Among primates, only Old World monkeys, the great apes, and humans have a third pigment gene&emdash;New World monkeys have only one X-linked pigment gene. Comment on the following three hypotheses: One of the two visual pigment loci on the X chromosome originated in a gene duplication event. The gene duplication event occurred after New World and Old World monkeys had diverged from a common ancestor, which had two visual pigment genes. Human males with a mutated form of the red or green pigment gene experience the same color vision of our male primate ancestors. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
17.	Chromosome number can evolve by smaller-scale changes than duplication of entire chromosome sets. For example, domestic horses have 64 chromosomes per diploid set while Przewalski's horse, an Asian subspecies, has 66. Przewalski's horse is thought to have evolved from an ancestor with chromosomes. The question is, Where did its extra chromosome pair originate? It seems unlikely that an entirely new chromosome pair was created de novo in Przewalski's horse. To generate a hypothesis explaining the origin of the new chromosome in Przewalski's horse, examine the adjacent figure. The drawing shows how certain chromosomes synapse in the hybrid offspring of a domestic horse–Przewalski's horse mating (Short et al. 1974). The remaining chromosomes show a normal 1:1 pairing. Do you think this sort of gradual change in chromosome number involves a change in the actual number of genes present, or just rearrangement of the same number of genes? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.