Exam 23: Evolutionary Processes

When imbalances occur in the sex ratio of sexual species that have two sexes (that is, other than a 50:50 ratio), the members of the minority sex often receive a greater proportion of care and resources from parents than do the offspring of the majority sex. This is most clearly an example of ________.

For a biologist studying a small fish population in the lab, which Hardy-Weinberg condition is easiest to meet?

Although each of the following has a better chance of influencing gene frequencies in small populations than in large populations, which one most consistently requires a small population as a precondition for its occurrence?

Use the following information to answer the question(s) below. Martin Wikelski and L. Michael Romero (Body size, performance, and fitness in Galápagos marine iguanas, Integrative and Comparative Biology 43 [2003]: 376-86) measured the snout-to-vent (anus) length of Galápagos marine iguanas and observed the percent survival of different-sized animals, all of the same age. The graph shows the log snout-vent length (SVL, a measure of overall body size) plotted against the percent survival of these different-size classes for males and females. -Currently, the only predators of Galápagos marine iguanas are Galápagos hawks. Iguana body size is not correlated with risk of hawk predation, although small iguanas can sprint faster than large iguanas. If predators (for example, cats) that preferentially catch and eat slower iguanas are introduced to the island, iguana body size is likely to ________ in the absence of other factors; the iguanas would then be under ________ selection.

Cystic fibrosis is a genetic disorder in homozygous recessive (ff) humans that typically significantly reduces life expectancy. Over time, we would expect the f allele frequency to ________ for this trait.

When nonrandom mating occurs in a population so that individuals prefer to mate with similar individuals, allele frequencies should

Which of the following statements best summarizes evolution by natural selection as it is viewed today?

Genetic variation ________.

Cystic fibrosis is a genetic disorder in homozygous recessives that causes death during the teenage years. If 9 in 10,000 newborn babies have the disease, what are the expected frequencies of the dominant (A1) and recessive (A2) alleles according to the Hardy-Weinberg model?

Which of the graphs shown best represents the relationship between the intensity of directional selection and the genetic variation present within a population?

Use the following information to answer the question(s) below. Martin Wikelski and L. Michael Romero (Body size, performance, and fitness in Galápagos marine iguanas, Integrative and Comparative Biology 43 [2003]: 376-86) measured the snout-to-vent (anus) length of Galápagos marine iguanas and observed the percent survival of different-sized animals, all of the same age. The graph shows the log snout-vent length (SVL, a measure of overall body size) plotted against the percent survival of these different-size classes for males and females. -Examine the accompanying figure. What type of selection for body size appears to be occurring in these marine iguanas?

Use the following information to answer the question below. In 1983, a population of dark-eyed junco birds became established on the campus of the University of California, San Diego (UCSD), which is located many miles from the junco's normal habitat in the mixed-coniferous temperate forests in the mountains. Juncos have white outer tail feathers that the males display during aggressive interactions and during courtship displays. Males with more white in their tail are more likely to win aggressive interactions, and females prefer to mate with males with more white in their tails. Females have less white in their tails than do males and display it less often. (Pamela J. Yeh. 2004. Rapid evolution of a sexually selected trait following population establishment in a novel habitat. Evolution 58[1]:166-74.) Refer to the paragraph on dark-eyed junco birds. The UCSD campus male junco population tails were, on average, 36 percent white, whereas the tails of males from nearby mountain populations averaged 40-45 percent white. If this observed trait difference were due to a difference in the original colonizing population, it would most likely be due to ________.

Genetic drift occurs in a population. Which of the following statements might be TRUE?

Use the following information to answer the question(s) below. Martin Wikelski and L. Michael Romero (Body size, performance, and fitness in Galápagos marine iguanas, Integrative and Comparative Biology 43 [2003]: 376-86) measured the snout-to-vent (anus) length of Galápagos marine iguanas and observed the percent survival of different-sized animals, all of the same age. The graph shows the log snout-vent length (SVL, a measure of overall body size) plotted against the percent survival of these different-size classes for males and females. -Wikelski and Romero (2003) found that large marine iguanas had higher reproductive success than smaller iguanas did. However, the large iguanas were generally in poor body condition because they could not eat enough; at higher temperatures, their foraging efficiency improved, allowing them to eat more. Thus, Wikelski and Romero hypothesized that iguana size will ________ as global warming gradually increases air and water temperatures in the Galápagos Islands.

In a small population of alpine foxes, you observe increased ear length over a 10-year period. Can you conclude that increase in ear length is advantageous in this population?

A researcher wants to know if gene flow is contributing to evolution of drought tolerance of pitcher plants in a specific bog. As a control, she should

In seedcracker finches from Cameroon, small- and large-billed birds specialize in cracking soft and hard seeds, respectively. If long-term climatic change resulted in all seeds becoming hard, what type of selection would then operate on the finch population?

Suppose 64 percent of a remote mountain village can taste phenylthiocarbamide (PTC) and must, therefore, have at least one copy of the dominant PTC taster allele. If this population conforms to Hardy-Weinberg expectations for this gene, what percentage of the population must be heterozygous for this trait?

An earthquake decimates a ground-squirrel population, killing 98 percent of the squirrels. The surviving population happens to have broader stripes, on average, than the initial population. If broadness of stripes is genetically determined, what effect has the ground-squirrel population experienced during the earthquake?

The Dunkers are a religious group that moved from Germany to Pennsylvania in the mid-1700s. They do not marry with members outside their own immediate community. Today, the Dunkers are genetically unique and differ in gene frequencies, at many loci, from all other populations, including those in their original homeland. Which of the following likely explains the genetic uniqueness of this population?