Exam 6: The Ways of Change: Drift and Selection

You are studying a population of 100 flowers that has two alleles at a locus for flower color, blue (B) and green (G). There are 15 individuals with the BB genotype, 70 individuals with the BG genotype, and 15 individuals with the GG genotype. (a) What are the allele frequencies of B and G in the starting population? Show your calculations. (b) Is this population in Hardy-Weinberg equilibrium? Show your calculations. (c) Given the results of part b and the distribution of genotypes, offer a hypothesis that could explain the results. Explain your reasoning.

Below you see graphs that depict the change in frequency of a neutral allele in four populations that differ in size. Which population would you predict is the smallest?

Genetic drift

In which of the scenarios below is a population more likely to evolve?

Many plant species are hermaphroditic and run the risk of self-mating. Some species carry self-incompatibility alleles that can prevent this from occurring. If a pollen grain with self-incompatibility allele S₁ lands on a stigma that also carries the S₁ allele, the pollen will not germinate and fertilization does not occur. Thus, this mechanism not only prevents selfing, but also has the unfortunate effect of preventing mating with any other plant that carries the same allele. However, if the pollen lands on a stigma of a plant with a different allele, fertilization occurs. Imagine a population of plants in which the allele frequency of S₁ = 0.9 and the allele frequency of S₂ = 0.1. All other things being equal, individuals with the ____ allele will have higher fitness on average. This is an example of ______.

Inbreeding

Tasmanian devils once inhabited most of present-day Australia, but only an isolated population on the island of Tasmania has survived to the present day. Which of the following processes has likely affected Tasmanian devils as a result of this history?

The frequency of a slightly deleterious allele maintained at an equilibrium frequency by mutation-selection balance would be higher

The graph below shows the change in allele frequency for a beneficial allele over time (the x axis shows generations). Based on the shape of the curve, this allele is most likely

Alleles are

In a population of butterflies that has two alleles at a locus for spots, no spots (N) and spots (S), there are 20 individuals with the NN genotype, 40 with the NS genotype, and 40 with the SS genotype. What is the frequency of N in the population?

Bighorn sheep occupy a range that extends from Canada to Mexico; however, this range is not continuous because the sheep prefer steep rocky cliffs, which are often spatially isolated. This is an example of

How does "random mating" affect population genetics studies?

Assuming that a deleterious allele is maintained in a population by mutation-selection balance, which scenario below describes the case where you would expect the equilibrium frequency of the allele to be highest?

The study of allele frequencies and distributions is

You collect the following data on genotypes for a sunflower population: AA: 40, AB: 20, BB: 40. Based on Hardy-Weinberg predictions you expected the following numbers: AA: 25, AB: 50, BB: 25. Which of the following is a plausible explanation for the deviation?

Which of the following is not true about a fixed genetic locus?

How might population structure affect evolution?

In the founder effect,

If p = 0.8, what is the frequency of heterozygotes in a population, assuming Hardy-Weinberg equilibrium?