Review Quiz #4
Genetics and Evolution
Which of the following best explains the differences in the armor of the Lake Washington stickleback population summarized in Figure 1 ?
A) Analysis of somatic cells using chromosomal staining and light microscopy indicates that stickleback fish have a diploid number of 42.
(B) Stickleback males from natural freshwater populations are typically more aggressive when competing for mates than are stickleback males from laboratory-bred populations.
(C) Fish exhibiting the low-plated phenotype were selected against in the Lake Washington stickleback population over the last 50 years.
(D) Migration of individuals from other freshwater environments to Lake Washington led to gene flow between populations that were once geographically isolated.
A completely-plated stickleback from a marine population was mated to a low-plated stickleback from a freshwater population. The resulting F1 hybrids all displayed a completely plated phenotype. When the F1 hybrids were allowed to interbreed, the resulting F2 generation included completely plated offspring and low-plated offspring in an approximate 3:1 ratio. Which of the following conclusions is best supported by the results of the breeding experiments?
(A) Phenotypic variation in the F2 generation suggests that armor morphology is controlled by many alleles of a single gene.
(B) The completely-plated phenotype is controlled by a dominant allele of a single gene.
(C) Armor loss is an acquired characteristic that is affected by one or more environmental factors.
(D) Patterns of armor plating in stickleback populations are regulated by sex-specific signals.
Prior to 1960, Lake Washington was highly polluted and underwater visibility was limited to one or two meters. In the late 1960s, a large cleanup effort reduced pollution, resulting in visibility that increased to six to seven meters by 1976. Which of the following best explains how the change in underwater visibility affected armor plating in Lake Washington sticklebacks between 1957 and 1976 ?
(A) Higher visibility allowed sticklebacks to increase their food consumption to make armor production easier.
(B) Higher visibility made the sticklebacks more susceptible to large-toothed predators in the lakes, giving complete armor a selective advantage.
(C) Clearer water allowed sunlight to penetrate to deeper depths, so the sticklebacks had to increase the amount of armor to protect themselves from the resulting increase in water temperature.
(D) Clearer water contained fewer of the molecular building blocks needed for armor production, so sticklebacks showed a reduction in the amount of armor.
Evolution of a new trait typically takes many generations. Yet a dramatic shift in the extent of armor plating in the Lake Washington stickleback population occurred in the 50 years following the cleanup of the lake. Which of the following best describes the mechanism of the rapid evolution of the armor phenotype in the Lake Washington sticklebacks?
(A) Pollutants in Lake Washington forced the sticklebacks to increase their mutation rate.
(B) The rapid change in the Lake Washington ecosystem required individual sticklebacks to evolve complete armor quickly.
(C) The increase in visibility in Lake Washington allowed sticklebacks to visually select mates with low armor.
(D) New selective pressures favored individuals with the plated phenotype, causing the plated allele frequency in the population to quickly increase.
The phylogenetic trees in Figures 2 and 3 depict two different phylogenies of the same populations of sticklebacks. Which of the following questions will best help determine which tree represents the most accurate phylogeny?
(A) Is the EDA gene as representative of the differences between the populations as the 25 random genes that were examined for Figure 3 ?
(B) Are the low-plated populations found only in freshwater and the high-plated populations found only in saltwater environments?
(C) Is the common ancestor of the organisms represented in Figure 2 different from the common ancestor of the organisms represented in Figure 3 ?
(D) Is the expression level of the EDA gene analyzed in Figure 2 significantly greater than the expression levels of the 25 genes analyzed in Figure 3 ?
Researchers observe a large population of birds on a remote island. Birds in the population are found to have either red crest feathers or white crest feathers on their heads. Genetic analysis indicates that the allele for red crest feathers is dominant over the allele for white crest feathers. In a survey of the population, the researchers determine the frequencies of the crest-feather phenotypes. The results of the survey are shown in the table above. Assuming that the bird population is in Hardy- Weinberg equilibrium, what proportion of future populations is expected to be heterozygous for the allele controlling crest feather color? Give your answer as a value between 0 and 1, rounded to two decimal places.
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