Question 1

What is true of natural selection?

Accepted Answer

Natural selection does not create mutations, but it can preserve and distribute beneficial mutations that occur randomly. Furthermore, harmful mutations can be eliminated through other processes such as genetic drift or genetic disorders.

Question 2

Blue light is a portion of the visible spectrum that penetrates deep into bodies of water. Ultraviolet (UV) light, though, can penetrate even deeper. A gene within a population of marine fish that inhabits depths from 500 m to 1,000 m has an allele for a photopigment that is sensitive to UV light, and another allele for a photopigment that is sensitive to blue light. Which of the graphs in Figure 21.1 best depicts the predicted distribution of these alleles within a population if the fish that carry these alleles prefer to locate themselves where they can see best?  Figure 21.1

Accepted Answer

The answer of Blue light is a portion of the...

Question 3

There are those who claim that the theory of evolution cannot be true because the apes, which are supposed to be closely related to humans, do not likewise share the same large brains, capacity for complicated speech, and tool-making capability. They reason that if these features are generally beneficial, then the apes should have evolved them as well. Which of these provides the best argument against this misconception?

Accepted Answer

The answer of There are those who claim that the...

Question 4

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?

Accepted Answer

This scenario describes an evolutionary arms race between bacteria and bacteriophages, where both parties adapt over time to counter each other's defenses. This dynamic interaction would likely result in fluctuating populations of methylated and nonmethylated strains among both bacteria and bacteriophages, rather than the fixation of one type of DNA in either group.

Question 5

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

Accepted Answer

The statement suggests that natural selection can only modify existing structures rather than creating entirely new ones. This is in line with the principle of descent with modification, which forms the basis of evolution by natural selection.

Question 6

When imbalances occur in the sex ratio of sexual species that have two sexes (i.e., 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

Accepted Answer

This is an example of frequency-dependent selection, where the fitness of a phenotype depends on its frequency relative to other phenotypes in a given population. In this case, the rarity of one sex increases its reproductive value, leading to increased parental investment.

Question 7

Which of the following is most likely to produce an African butterfly species in the wild whose members have one of two strikingly different color patterns?

Accepted Answer

Disruptive selection favors extreme traits over intermediate ones, which can lead to the development of two or more distinct phenotypes within a population. In the case of the African butterfly species, disruptive selection could lead to individuals with either one of two strikingly different color patterns.

Question 8

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

Accepted Answer

The trend toward decreasing larynx size in adult females and increasing larynx size in adult males indicates sexual dimorphism was developing over time in these species. This sexual dimorphism is likely the result of sexual selection, as deeper voices may have conferred some sort of advantage in male-male competition or attraction to females. This trend is not consistent with stabilizing selection or direct selection on genotype versus phenotype.

Question 9

In the wild, male house finches (Carpodus mexicanus) vary considerably in the amount of red pigmentation in their head and throat feathers, with colors ranging from pale yellow to bright red. These colors come from carotenoid pigments that are found in the birds' diets; no vertebrates are known to synthesize carotenoid pigments. Thus, the brighter red the male's feathers are, the more successful he has been at acquiring the red carotenoid pigment by his food-gathering efforts (all other factors being equal). During breeding season, one should expect female house finches to prefer to mate with males with the brightest red feathers. Which of the following is true of this situation?

Accepted Answer

Alleles that promote more efficient acquisition of carotenoid-containing foods by males and alleles that promote more effective deposition of carotenoid pigments in the feathers of males should increase over the course of generations, as they confer a selective advantage to males with brighter red feathers. This creates directional selection for bright red feathers in males, as females preferentially choose to mate with males with brighter red feathers during breeding season. Therefore, three of the statements are correct.

Question 10

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

Accepted Answer

The process described in the passage involves frequency-dependent selection, where the prevalence of one genotype (methylated bacteriophages or unmethylated bacteria) affects the fitness of the other genotype. This creates a fluctuating selection pressure that can result in evolutionary change over time. The other options (B, C, D, E) do not accurately describe the dynamic interaction between the bacteria and bacteriophage populations.

Question 11

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?

Accepted Answer

Stabilizing selection favors individuals with intermediate traits, while reducing the fitness of individuals with extreme traits. In this case, starlings producing fewer or more than four to five eggs have extreme traits and reduced fitness.

Question 12

The same gene that causes various coat patterns in wild and domesticated cats also causes a cross-eyed condition in these cats, the cross-eyed condition being slightly maladaptive. In a hypothetical environment, the coat pattern that is associated with crossed eyes is highly adaptive, with the result that both the coat pattern and the cross-eyed condition increase in a feline population over time. Which statement is supported by these observations?

Accepted Answer

This scenario illustrates that phenotype (coat pattern and eye-muscle tone) is often the result of compromise rather than being solely adaptive or maladaptive. The presence of the same gene causing both the coat pattern and the slightly maladaptive cross-eyed condition suggests that there is a trade-off between these two traits. In the hypothetical environment where the coat pattern associated with crossed eyes is highly adaptive, there is a conflict between the benefits and drawbacks of this gene. This situation supports the idea that phenotype is often the result of compromise.

Question 13

If the original finches that had been blown over to the Galápagos from South America had already been genetically different from the parental population of South American finches, even before adapting to the Galápagos, this would have been an example of

Accepted Answer

The answer of If the original finches that had been...

Question 14

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?

Accepted Answer

Directional selection. In this scenario, the selection pressure would favor only the large-billed finches that can crack hard seeds, as soft seeds would no longer be available. Over time, the frequency of the large-billed phenotype would increase while the small-billed phenotype would decrease or disappear. This is an example of directional selection, where the trait distribution shifts towards one end of the spectrum.

Question 15

Sexual dimorphism is most often a result of

Accepted Answer

Sexual dimorphism refers to differences in appearance or behavior between males and females of the same species. Intersexual selection, also known as mate choice, is a common cause of sexual dimorphism because individuals with certain traits are preferred as mates by individuals of the opposite sex. This can lead to the evolution of traits that are more attractive to potential mates, which can vary between males and females.

Question 16

The recessive allele that causes phenylketonuria (PKU) is harmful, except when an infant's diet has appropriate levels of the amino acid phenylalanine. What maintains the presence of this harmful allele in a population's gene pool?

Accepted Answer

Diploidy allows recessive alleles to be carried in heterozygous individuals without being expressed, maintaining them in the gene pool.

Question 17

Heterozygote advantage should be most closely linked to which of the following?

Accepted Answer

Heterozygote advantage occurs when individuals with two different alleles have a higher fitness than individuals with either of the two homozygous genotypes. Stabilizing selection favors this middle-ground heterozygous state over the extremes of homozygosity. Therefore, heterozygote advantage is most closely linked to stabilizing selection.

Question 18

During breeding season, one should expect female house finches to prefer to mate with males with the brightest red feathers. Which of the following terms are appropriately applied to this situation?

Accepted Answer

All three of the given terms are appropriate to describe the situation described. Sexual selection refers to the process of individuals within a species competing for mates and/or attracting mates. Mate choice refers to the ability of individuals to choose their own mates. Intersexual selection refers specifically to situations where one sex (usually females) choose mates based on specific traits or behaviors of the opposite sex. In the given scenario, female house finches are choosing to mate with males with the brightest red feathers, making it a clear example of intersexual selection and mate choice.

Question 19

Arrange the following from most general (i.e., most inclusive) to most specific (i.e., least inclusive): 1. natural selection
2) microevolution
3) intrasexual selection
4) evolution
5) sexual selection

Accepted Answer

Evolution is the most general concept, encompassing all changes in the gene pool of a population over time. Microevolution refers to small-scale changes within species. Natural selection is a mechanism of evolution, explaining how traits become more or less common. Sexual selection, a subset of natural selection, explains how mate choice affects evolution. Intrasexual selection, a type of sexual selection, specifically deals with competition among the same sex for mates.

Question 20

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

Accepted Answer

Evolution is the process of differential survival and reproduction of organisms with the most-fit phenotypes, leading to changes in the genetic makeup of populations over time. The idea of acquired characteristics, where traits are developed during an organism's lifetime and passed on to offspring, has been discredited. Gene flow is a separate process that involves the movement of genetic material between populations, but it is not synonymous with evolution. The descent of humans from great apes is a specific example of the broader concept of evolution.

Quiz 21: The Evolution of Populations