Chapter 23 Questions

If individuals tend to mate within a subset of the population, there is ________.

no random mating

Which of the following is the best modern definition of evolution?

descent with modification

Which of the following descriptions illustrates phenotype variation caused by environment?

diet of caterpillars changes their morphology

Microevolutions occur when ________.

changes in allele frequencies in a population occur over generations

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 equation?

f(A1) = 0.9700, f(A2) = 0.0300

Adult male humans generally have deeper voices than do adult female humans, which is the direct result of higher levels of testosterone causing growth of the larynx. If the fossil records of apes and humans alike show a trend toward decreasing larynx size in adult females and increasing larynx size in adult males, then _____.

sexual dimorphism was evolving over time in these species

According to the Hardy-Weinberg theorem, the frequencies of alleles in a population will remain constant if _____ is the only process that affects the gene pool.

sexual reproduction

Which mechanism produces variation for evolution by shuffling existing alleles?

sexual reproduction

Which one of the following conditions would allow gene frequencies to change by chance?

small populations

Which one of these processes describes bottleneck effect?

sudden change in environments that alters gene frequency of a population

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

0.09

In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.2. What is the frequency of individuals that are heterozygous for this allele?

0.32

A fruit fly population has a gene with two alleles, A1 and A2. Tests show that 70% of the gametes produced in the population contain the A1 allele. If the population is in Hardy-Weinberg equilibrium, what proportion of the flies carry both A1 and A2?

0.42

What is the estimated frequency of allele A in the gene pool?

0.50

What proportion of the population is probably heterozygous (Aa) for this trait?

0.50

In peas, a gene controls flower color such that R = purple and r = white. In an isolated pea patch, there are 36 purple-flowering plants and 64 white-flowering plants. Assuming Hardy-Weinberg equilibrium, what is the value of q for this population?

0.80

In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.1. What is the frequency of individuals with AA genotype?

0.81

In some jacana species, males take care of the eggs and young, and females compete among themselves for territories that contain one to several males. Female jacanas are significantly larger than males. Which of these statements would you predict to be true of this bird species?1. Male jacana fitness is primarily limited by ability to take care of eggs and raise young.2. Female jacana fitness is limited by the number of males in her territory with which a female mates.3. Variation in reproductive success should be greater in male jacanas than in females.4. Variation in reproductive success should be greater in female jacanas than in males.5. Males and females have equal variation in reproductive success.

1, 2, and 4

Suppose a BB female mouse mates with a Bb male mouse. Which of the following represents the probabilities of each genotype occurring among their offspring?

1/2 BB, 1/2 Bb Submit

One out of 10,000 babies born in North America is affected by cystic fibrosis, a recessive condition. Assuming that the North American human population is in Hardy-Weinberg equilibrium for this trait, what percentage of the population is heterozygous for this trait? (Remember the equation for a population in Hardy-Weinberg equilibrium: p2 + 2pq + q2 = 1.)

2%

Arrange the following in order from most general to most specific.1 natural selection2. microevolution3. intrasexual selection4. evolution5. sexual selection

4, 2, 1, 5, 3

Suppose 64% 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 equilibrium for this gene, what percentage of the population must be heterozygous for this trait?

48%

You read about soapberry bugs and select the correct statement describing relative fitness in these individuals.

A soapberry bug with high relative fitness has a relatively high number of offspring that survive to reproductive age.

Which statement about variation is true?

All new alleles are the result of nucleotide variability.

You sample a population of butterflies and find that 56% are heterozygous at a particular locus. What should be the frequency of the recessive allele in this population?

Allele frequency cannot be determined from this information. Submit

Suppose that a gene for coat color in mice has two alleles, B and b, where B is completely dominant and encodes a black coat color, and b is recessive and encodes a brown coat color. A mouse that is heterozygous has genotype _____, and its phenotype is _____.

Bb; black

Why does the fitness of a phenotype depend on frequency-dependent selection?

Because frequency-dependent selection acts against extreme phenotypes. Submit

Which of the following is a testable hypothesis that would explain the differences in caterpillar appearance observed in this population?

Differences in diet trigger the development of different types of caterpillars.

Which statement about the beak size of finches on the island of Daphne Major during prolonged drought is true?

Each bird's survival was strongly influenced by the depth and strength of its beak as the drought persisted. Submit

Swine are vulnerable to infection by bird flu virus and human flu virus, which can both be present in an individual pig at the same time. When this occurs, 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 new virus, and if the new virus is introduced to an environment lacking Tamiflu, then what is most likely to occur?

If the Tamiflu-resistance gene involves a cost, it will experience directional selection leading to reduction in its frequency.

How does diploidy help to preserve genetic variation?

It allows recessive alleles that may not be favored in the current environment to be preserved in the gene pool by propagation in heterozygotes.

What is true of microevolution?

It is the kind of evolution that can change the relative abundance of a particular allele in a gene pool over the course of generations.

The restriction enzymes of 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, this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA. Over the course of evolutionary time, what should occur?

Methylated and nonmethylated strains should be maintained among both bacteria and bacteriophages, with ratios that vary over time. Submit

In 1986, a nuclear power accident in Chernobyl, USSR (now Ukraine), led to high radiation levels for miles surrounding the plant. The high levels of radiation caused elevated mutation rates in the surviving organisms, and evolutionary biologists have been studying rodent populations in the Chernobyl area ever since. Based on your understanding of evolutionary mechanisms, which of the following most likely occurred in the rodent populations following the accident?

Mutation led to increased genetic variation.

Is this population in Hardy-Weinberg equilibrium?

No; there are more homozygotes than expected.

The fruit fly Drosophila melanogaster has an allele that confers resistance to DDT and similar insecticides. Laboratory strains of D. melanogaster have been established from flies collected in the wild in the 1930s (before the widespread use of insecticides) and the 1960s (after 20 years of DDT use). Lab strains established in the 1930s have no alleles for DDT resistance. In lab strains established in the 1960s, the frequency of the DDT-resistance allele is 37%. Which statement is correct?

The evolutionary fitness associated with the heritable trait of DDT resistance changed once DDT use became widespread. Submit

What is the most reasonable conclusion that can be drawn from the fact that the frequency of the recessive trait (aa) has not changed over time?

The two phenotypes are about equally adaptive under laboratory conditions.

Which statement correctly describes the role of chance in evolution?

The ultimate source of new alleles is mutation, random changes in the nucleotide sequences of an organism's DNA.

Which of the following treatment options would most likely avoid the evolution of drug-resistant HIV (assuming no drug interactions or side effects)?

Use moderate doses of NA and two different PIs at the same time for several months. Submit

The UCSD campus male junco population tails were, on average, 36% white, whereas the tails of males from nearby mountain populations averaged 40-45% white. If this observed trait difference were due to a difference in the original colonizing population, it would most likely be due to ________.

a founder effect

An earthquake decimates a ground-squirrel population, killing 98% 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?

a genetic bottleneck

Consider the following mutations to the nucleotide sequence of a gene. Which of these mutations would not alter the reading frame of the gene's genetic message?

a single nucleotide-pair substitution

Genetic drift produces variation for evolution when ________.

chance events cause allele frequencies to fluctuate unpredictably

In evolutionary terms, an organism's fitness is measured by its _____.

contribution to the gene pool of the next generation

You are maintaining a small population of fruit flies in the laboratory by transferring the flies to a new culture bottle after each generation. After several generations, you notice that the viability of the flies has decreased greatly. Recognizing that small population size is likely to be linked to decreased viability, the best way to reverse this trend is to _____.

cross your flies with flies from another lab

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 preferably 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.

decrease; directional

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

decreased genetic difference between the two populations

Blue poppies native to China were grown at a plant-breeding center in California. The plants with the thickest leaves were most likely to survive and reproduce in the drier climate. After several generations, the percentage of thick-leaved plants had increased by 42%. This adaptation of the poppies to their new environment is due to _____.

directional selection

In a very large population, a quantitative trait has the following distribution pattern. If there is no gene flow, the curve shifts to the left or to the right, and the population size consequently increases over successive generations, which of the following is most likely occurring?

directional selection

In the United States, the parasite that causes malaria is not present, but it is present in African-Americans whose ancestors were from equatorial Africa. What should be happening to the sickle-cell allele in the United States, and what should be happening to it in equatorial Africa?

directional selection; stabilizing selection Submit

A biologist doing a long-term study on a wild spider population observes increased variation in silk thickness. Which of the following could the spider population be experiencing?

disruptive selection

Three-spined stickleback fish (Gasterosteus aculeatus) show substantial heritable 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

What situation most likely explains the occasional high frequency of certain inherited disorders among human populations established by a small population?

founder effect

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?

founder effect and genetic drift

The restriction enzymes of 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, this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA. The outcome of the conflict between bacteria and bacteriophage at any point in time results from _____.

frequency-dependent selection

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 _____.

frequency-dependent selection

Comparisons 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. This indicates that interbreeding occurred before human migration further east. What process of population genetics generated these results?

gene flow

Over time, the movement of people on Earth has steadily increased. This has altered the course of human evolution by increasing _____.

gene flow

If the nucleotide variability of a locus equals 0%, what is the gene variability and number of alleles at that locus?

gene variability = 0%; number of alleles = 1

Allele frequencies in a gene pool may shift randomly and by chance. What is this random shift called?

genetic drift

One of the following is NOT a source of genetic variation.

genetic drift

Which Hardy-Weinberg condition is affected by population size?

genetic drift

There are 40 individuals in population 1, all with genotype A1A1, and there are 25 individuals in population 2, all with genotype A2A2. Assume that these populations are located far from each other and that their environmental conditions are very similar. Based on the information given here, the observed genetic variation is most likely an example of

genetic drift.

In the formula for determining a population's genotype frequencies, the "2" in the term 2pq is necessary because _____.

heterozygotes can come about in two ways

In the formula for determining a populations genotype frequencies, the "pq" in the term 2pq is necessary because _____.

heterozygotes have two alleles

Homozygotes with two sickle-cell alleles are selected against because of mortality. However, heterozygotes for sickle-cell allele experience little effects of sickle allele and are more likely to survive malaria. The net effect of this exposure produced evolutionary change in areas where malaria is endemic by ________.

increasing sickle-cell allele frequency

Natural selection changes allele frequencies because some _______ survive and reproduce more successfully than others.

individuals

If one builds a canal linking a predator-rich pond to a predator-poor pond, then what type of selection should subsequently be most expected among the mosquitofish in the original predator-rich pond, and what type should be most expected among the mosquitofish in the formerly predator-poor pond?

less-intense directional selection; more-intense directional selection Submit

Genetic variation ________.

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

The original source of all genetic variation is _____.

mutation

The UCSD campus male junco population tails are about 36% white, whereas the tails of males from nearby mountain populations are about 40-45% white. The founding stock of UCSD birds was likely from the nearby mountain populations because some of those birds overwinter on the UCSD campus each year. Population sizes on the UCSD campus have been reasonably large, and there are significant habitat differences between the UCSD campus and the mountain coniferous forests; UCSD campus has a more open environment (making birds more visible) and a lower junco density (decreasing intraspecific competition) than the mountain forests. Given this information, which of the following evolutionary mechanisms do you think is most likely responsible for the difference between the UCSD and mountain populations?

natural selection

What is the only evolutionary mechanism that consistently leads to adaptive evolution?

natural selection

A proficient engineer can easily design skeletal structures that are more functional than those currently found in the forelimbs of such diverse mammals as horses, whales, and bats. The actual forelimbs of these mammals do not seem to be optimally arranged because _____.

natural selection is generally limited to modifying structures that were present in previous generations and in previous species

Anopheles mosquitoes, which carry the malaria parasite, cannot live above elevations of 5,900 feet. In addition, oxygen availability decreases with higher altitude. Consider a hypothetical human population that is adapted to life on the slopes of Mt. Kilimanjaro in Tanzania, a country in equatorial Africa. Mt. Kilimanjaro's base is about 2,600 feet above sea level and its peak is 19,341 feet above sea level. If the incidence of the sickle-cell allele in the population is plotted against altitude (feet above sea level), which of the following distributions is most likely, assuming little migration of people up or down the mountain?

negative linear

The higher the proportion of loci that are "fixed" in a population, the lower are that population's ________.

nucleotide variability and average heterozygosity

Examine the figure. What type of selection for body size appears to be occurring in these marine iguanas?

stabilizing selection

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

stabilizing selection

Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus, _____.

the allele's frequency should not change from one generation to the next

Soon after the island of Hawaii rose above the sea surface (somewhat less than one million years ago), the evolution of life on this new island should have been most strongly influenced by ________.

the founder effect

The inability of organisms to evolve anything that could be an advantage reflects ________.

the limits of choices of genes within a species

The evolutionary effects of genetic drift are greatest when _____.

the population size is small

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

the reshuffling of alleles in sexual reproduction.