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Exam 24: Population Genetics

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Question 1

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Genetic drift is change in allelic frequency due to chance factors. The amount of change in allelic frequency due to genetic drift is inversely related to the effective population size (the equivalent number of breeding adults in a population) . -Which of the following statements is an example of genetic drift?

A) Allele g for fat production increases in a small population because birds with more body fat have higher survivorship in a harsh winter.
B) Random mutation increases the frequency of allele A in one population but not in another.
C) Allele R reaches a frequency of 1.0 because individuals with genotype rr are sterile.
D) Allele m is lost when a virus kills all but a few individuals and just by chance none of the survivors possess allele m.

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Question 2

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Natural selection is the differential reproduction of genotypes. It is measured as fitness, which is the reproductive success of a genotype compared with other genotypes in a population. -The average numbers of offspring produced by three genotypes are: GG = 6; Gg = 3, gg = 2. What is the fitness of Gg?

A) 3
B) 0.5
C) 0.3
D) 0.27

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Question 3

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The Hardy-Weinberg law describes how reproduction and Mendelian principles affect the allelic and genotypic frequencies of a population. -Which statement is not an assumption of the Hardy-Weinberg law?

Migration causes changes in the allelic frequency of a population by introducing alleles from other populations. The magnitude of change due to migration depends on both the extent of migration and the difference in allelic frequencies between the source and the recipient populations. Migration decreases genetic differences between populations and increases genetic variation within populations. -Each generation, 10 random individuals migrate from population A to population B. What will happen to allelic frequency q as a result of migration when q is equal in populations A and B?

Population genetics concerns the genetic composition of a population and how it changes with time. The gene pool of a population can be described by the frequencies of genotypes and alleles in the population. -What are some advantages of using allelic frequencies to describe the gene pool of a population instead of using genotypic frequencies?

Recurrent mutation causes changes in the frequencies of alleles. At equilibrium, the allelic frequencies are determined by the forward and reverse mutation rates. Because mutation rates are low, the effect of mutation per generation is very small. -When a population is in equilibrium for forward and reverse mutation rates, which of the following is true:

Nonrandom mating alters the frequencies of the genotypes but not the frequencies of the alleles. Inbreeding is preferential mating between related individuals. With inbreeding, the frequency of homozygotes increases, whereas the frequency of heterozygotes decreases. -What is the effect of outcrossing on a population?

Although allelic frequencies cannot be calculated directly for traits that exhibit dominance, the Hardy-Weinberg law can be used to estimate the allelic frequencies if the population is in Hardy- Weinberg equilibrium for that locus. The frequency of the recessive allele will be equal to the square root of the frequency of the recessive trait. -In cats, all-white color is dominant over not all-white. In a population of 100 cats, 19 are all-white cats. Assuming that the population is in Hardy-Weinberg equilibrium, what is the frequency of the all-white allele in this population?

Natural selection changes allelic frequencies; the direction and magnitude of change depend on the intensity of selection, the dominance relations of the alleles, and the allelic frequencies. Directional selection favors one allele over another and eventually leads to fixation of the favored allele. Overdominance leads to a stable equilibrium with maintenance of both alleles in the population. Underdominance produces an unstable equilibrium because the heterozygote has lower fitness than those of the two homozygotes. -How does overdominance differ from directional selection?

The observed number of genotypes in a population can be compared with the Hardy-Weinberg expected proportions by using a goodness-of-fit chi-square test. -What is the expected frequency of heterozygotes in a population with allelic frequencies x and y that is in Hardy-Weinberg equilibrium?