Exam 23: Microevolution

An earthquake decimates a ground-squirrel population, killing 98% of the squirrels. The surviving population has broader stripes, on average, than the initial population. If broadness of stripes is genetically determined, which of the following processes most likely caused the change?

A large population of laboratory animals has been allowed to breed randomly for a number of generations. After several generations, 25% of the animals display a recessive trait (A2A2), the same percentage as at the beginning of the breeding program. The rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants. What is the most reasonable conclusion that can be drawn from the fact that the frequency of the recessive trait (A2A2) has not changed over time?

Which of the following processes best describes the cause of a bottleneck effect?

Natural selection changes allele frequencies because some ________ survive and reproduce better than others.

In some jacana (a bird) species, males take care of the eggs and young, and females compete with each other for territories that contain one to several males. Female jacanas are significantly larger than males. Which of these statements is likely NOT an accurate description of this bird species?

A biologist doing a long-term study on a wild spider population observes increased variation in silk thickness. Which of the following processes is the most likely to be affecting the spider population?

Which of the following results is the most likely outcome of increased gene flow between two populations?

In a Hardy-Weinberg population with two alleles A1 and A2 that are in equilibrium, the frequency of the allele A2 is 0.3. What is the frequency of individuals that are homozygous for this allele?

Researchers studying a small milkweed population note that some plants produce a toxin and other plants do not. They identify the gene responsible for toxin production. One allele (T1) codes for an enzyme that makes the toxin, and another allele (T2) codes for a nonfunctional enzyme that cannot produce the toxin. Heterozygotes produce an intermediate amount of toxin. The genotypes of a random sample of 200 individuals in the population were identified as shown in the table. Based on the genotypes in the sample, which is the best estimate of the allele frequencies in the total population?

Which of the following statements about evolutionary forces is accurate?

Most Swiss starlings (birds) produce four to five eggs in each clutch. Starlings producing more or less eggs have reduced fitness. Which of the following terms best describes this situation?

Restriction enzymes in bacteria protect the bacteria from successful attack by bacteriophages, whose genomes can be degraded by the restriction enzymes. The bacterial genomes are not vulnerable to these restriction enzymes because bacterial DNA is methylated. This situation selects for bacteriophages whose genomes are also methylated. As new strains of resistant bacteriophages become more prevalent, they in turn select for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA. Which of the following outcomes is most likely to occur over the course of evolutionary time?

Studies of Neanderthal DNA revealed that there are more similarities to non-African DNA than reference sequences from West Africans. Additionally, scientists found that Neanderthal DNA is as closely related to East Asians as to Europeans. These patterns indicate that interbreeding occurred before human migration further east. Which evolutionary force most likely generated these results?

A species of moth lays eggs on oak trees in spring and summer. Spring caterpillars eat oak flowers and look like oak flowers. Summer caterpillars eat oak leaves and look like twigs. To investigate how the same population of moths can produce such variable caterpillars, a researcher collected eggs from a population of moths and allowed them to hatch and grow under the conditions shown in the table below. Comparison of which treatments would allow the researcher to assess the effect of food type on caterpillar morphology?

A scientist samples a population of butterflies and finds that 56% are heterozygous at a particular locus. If the population is in Hardy-Weinberg equilibrium, what should be the frequency of the homozygous individuals in this population?

No two people are genetically identical, except for identical twins. The main source of genetic variation among humans is ________.

Pigs are vulnerable to infection by bird flu virus and human flu virus, both of which can be present in an individual pig at the same time. When both viruses infect a pig simultaneously, it is possible for genes from bird flu virus and human flu virus to be combined. If the human flu virus contributes a gene for Tamiflu resistance (Tamiflu is an antiviral drug) to the bird flu virus, and if this new virus is introduced to an environment lacking Tamiflu, then which of the following scenarios is most likely to occur?

Three-spined stickleback fish (Gasterosteus aculeatus) show substantial genetic variation in gill-raker length related to differences in their diets. Longer gill rakers appear to function better for capturing open-water prey, while shorter gill rakers function better for capturing shallow-water prey. Which of the following types of selection is most likely to be found in a large lake (open water in the middle and shallow water around the sides) with a high density of these fish?

The following questions are based on information from Yeh P., Rapid evolution of a sexually selected trait following population establishment in a novel habitat, Evolution 58(1):166-74 (2004). The Hawaiian Islands are the tops of undersea volcanoes in the Pacific Ocean. The oldest islands are the northwest-most islands. The islands get progressively younger to the southeast. Hawaii, the "big island," arose from the ocean less than one million years ago. Which of the following processes likely most strongly influenced the evolution of life on the big island when organisms first arrived?

Which of the following reasons best explains why separate populations of a given species are likely to vary genetically from one another?