ch 22, 23, 24

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 allele frequency of T1 is determined to be 0.6 and the allele frequency of T2 is 0.4. What is the expected frequency of heterozygotes if the population is in Hardy-Weinberg equilibrium?

0.48

Which of the following statements is accurate with regard to a population in Hardy-Weinberg equilibrium?

Allele frequencies should not change from one generation to the next.

which of the following conclusions is most consistent with the information in the evolutionary tree shown

Crocodiles are more closely related to hawks than to lizards.

Which of the following statements about genetic variation is accurate?

Genetic variation must be present in a population before natural selection can act upon the population.

The upper forelimbs of humans and bats have fairly similar skeletal structures, whereas the corresponding bones in whales have very different shapes and proportions. However, genetic data suggest that all three kinds of organisms diverged from a common ancestor at about the same time. Which of the following is the most likely explanation for these data?

Natural selection in an aquatic environment resulted in significant changes to whale forelimb anatomy.

Bird guides once listed the myrtle warbler and Audubon's warbler as distinct species. Recently, these birds have been classified as eastern and western forms of a single species, the yellow-rumped warbler. Which of the following pieces of evidence, if true, would be cause for this reclassification?

The two forms interbreed often in nature, and their offspring survive and reproduce well.

A farmer uses triazine herbicide to control pigweed in his field. For the first few years, the triazine works well and almost all the pigweed dies; however, after several years, the farmer sees more and more pigweed growing once again in the fields. Which of the following statements best explains the return of pigweed to the farmer's fields?

Triazine-resistant weeds were more likely to survive and reproduce than were non-resistant individuals.

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 bottleneck effect

Which of the following characteristics is most likely an adaptation?

bright colors of prairie flowers

Which of the following is the best definition of evolution on the smallest scale?

change in allele frequencies in a population over time

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?

disruptive selection

After a drought in 1977, researchers hypothesized that on the Galápagos Island Daphne Major, medium ground finches with large, deep beaks survived better than those with smaller beaks because they could more easily crack and eat the tough Tribulus cistoides fruits. A tourist company sets up reliable feeding stations with a variety of bird seeds (different types and sizes) so that tourists can get a better look at the finches. Which of the following events is now most likely to occur to finch beaks on this island?

increased variation in beak size and shape over time

Which of these conditions do NOT occur in populations evolving due to natural selection?

individuals pass on most traits that they acquire during their lifetime.

Which of the following characteristics are demonstrated by the production of sterile mules after female horses mate with male donkeys?

reduced hybrid fertility

If biological species are defined in terms of reproductive compatibility, which of the following factors determines the formation of a new species?

reproductive isolation

The largest unit within which gene flow can readily occur is a ________.

species