Question 1

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?

Accepted Answer

The change in the squirrel population's stripe broadness is most likely due to a bottleneck effect, which occurs when a significant portion of a population is suddenly eliminated, leaving a small, non-representative sample of the original population. The surviving squirrels' broader stripes indicate that the genetic diversity has been drastically reduced, and the characteristics of the surviving population may not reflect those of the original population.

Question 2

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?

Accepted Answer

The frequency of individuals homozygous for the allele A2 (A2A2) can be calculated using the Hardy-Weinberg principle as p^2, q^2, or 2pq for different genotypes, where p and q represent the frequencies of the two alleles, and p + q = 1. Given that the frequency of A2 is 0.3 (q = 0.3), the frequency of homozygous A2A2 individuals is q^2 = 0.3^2 = 0.09.

Question 3

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 percent 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 proportion of the population is most likely heterozygous (A1A2) for this trait?

Accepted Answer

Given that 25% of the population displays the recessive trait (A2A2), we can deduce that the frequency of the recessive allele (a2) is 0.5 (since the square root of 0.25 is 0.5). This means that the frequency of the dominant allele (A1) is also 0.5 to make up the total allele frequency of 1. Using the Hardy-Weinberg principle, the proportion of heterozygotes (2pq) in the population can be calculated as 2(0.5)(0.5) = 0.50, indicating that 50% of the population is most likely heterozygous (A1A2).

Question 4

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?

Accepted Answer

The constant frequency of the recessive trait suggests that both the dominant and recessive phenotypes have similar adaptive values in the laboratory environment, allowing them to persist in equal proportions over generations.

Question 5

A population of dark-eyed junco birds became established near the California coastline, 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.
The coastal male junco population tails were, on average, 36% white; whereas the tails of males from the mountain populations averaged 40-45% white. Which of the following factors is the most likely original cause of the difference between the populations if the trait is inherited?

Accepted Answer

The most likely original cause of the difference in tail coloration between the coastal and mountain junco populations is the founder effect. This occurs when a new population is established by a small number of individuals from a larger population, leading to reduced genetic variation and potentially different traits in the new population compared to the original one.

Question 6

In peas, a gene controls flower color such that R1 = purple and R2 = white. The purple allele is dominant to the white allele. 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?

Accepted Answer

In Hardy-Weinberg equilibrium, the frequency of the two alleles in a population can be represented as p^2 + 2pq + q^2 = 1, where p is the frequency of the dominant allele, and q is the frequency of the recessive allele. Since white-flowering plants are recessive, the frequency of the white-flowering phenotype (q^2) can be calculated from the proportion of white-flowering plants in the population. With 64 white-flowering plants out of a total of 100 plants, q^2 = 64/100 = 0.64. Taking the square root of 0.64 gives q = 0.8.

Question 7

A population of dark-eyed junco birds became established near the California coastline, 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.
Population sizes in the coastal areas have been reasonably large, and there are significant differences between the coastal and the mountain habitats. The coastal habitat is more open (making birds more visible) and has a lower junco density (decreasing intraspecific competition) than the mountain forests. Given this information, which of the following evolutionary mechanisms is the most likely cause of the difference between the coastal and mountain populations?

Accepted Answer

Natural selection is the most likely cause of the difference between the coastal and mountain populations because the coastal habitat's unique characteristics (more open, making birds more visible, and lower junco density) would favor juncos with more white in their tails for both aggressive interactions and mating success, leading to an evolutionary change in the population.

Question 8

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 allele frequencies at many loci from all other populations, including those in their original homeland. Which of the following mechanisms most likely explains the genetic uniqueness of this population?

Accepted Answer

The genetic uniqueness of the Dunkers is most likely explained by the founder effect and genetic drift. The founder effect occurs when a new colony is started by a few members of the original population, leading to a reduction in genetic variation and a change in allele frequencies in the new population. Genetic drift further influences allele frequencies in small, isolated populations, like the Dunkers, leading to genetic uniqueness over time.

Question 9

In which of the following situations would genetic drift most likely cause evolution?

Accepted Answer

Genetic drift refers to random fluctuations in the frequencies of alleles within a population's gene pool. It is most likely to cause evolution in small populations where chance events can significantly impact allele frequencies, as described in option B.

Question 10

Over time, humans have steadily increased their movements across the continents of the Earth. Which of the following results has most likely been derived from these movements?

Accepted Answer

Increased human movement across continents has facilitated the mixing of different populations, leading to increased gene flow. Gene flow is the transfer of genetic variation from one population to another, which can occur when individuals from different populations migrate and reproduce. This movement and subsequent interbreeding among diverse populations reduce genetic differences between populations, enhancing genetic diversity within populations.

Question 11

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 estimated frequency of allele A1 in the gene pool?

Accepted Answer

The frequency of the recessive allele (A2) is 0.5, since 25% of the population displays the recessive trait. The frequency of the dominant allele (A1) is therefore 1 - 0.5 = 0.5.

Question 12

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?

Accepted Answer

Gene flow is the correct answer because it refers to the transfer of genetic variation from one population to another. The presence of Neanderthal DNA in non-African human populations suggests that there was interbreeding between Neanderthals and early modern humans as they migrated out of Africa, which is a classic example of gene flow.

Question 13

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?

Accepted Answer

The answer of The following questions are based on information...

Question 14

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. Which of the following events most likely occurred in the rodent populations following the accident?

Accepted Answer

Mutation led to increased genetic variation. High levels of radiation can cause mutations in DNA, leading to genetic changes. In the context of evolutionary biology, these mutations can increase genetic variation within a population, providing a broader range of traits for natural selection to act upon.

Question 15

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

Accepted Answer

Increased gene flow between two populations typically results in decreased genetic difference between them, as genes from one population are introduced into the other, leading to a more homogenized gene pool.

Question 16

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

Accepted Answer

The bottleneck effect occurs when there's a drastic decrease in the size of a population, often due to a sudden environmental change or disaster, leading to a reduction in genetic diversity as the surviving population's gene pool becomes less varied.

Question 17

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?

Accepted Answer

The answer of A scientist samples a population of butterflies...

Question 18

The value of the Hardy-Weinberg equation is that it allows scientists to perform which of the following assessments?

Accepted Answer

The Hardy-Weinberg equation can be used to detect whether an evolutionary force is acting on a population by comparing the observed allele and genotype frequencies to the expected frequencies under the assumption of no evolution.

Question 19

In a Hardy-Weinberg population with two alleles A1 and A2 that are in equilibrium, the frequency of allele A2 is 0.1. What is the frequency of individuals with A1A1 genotype?

Accepted Answer

The frequency of allele A2 is 0.1, so the frequency of allele A1 is 1 - 0.1 = 0.9. The frequency of individuals with the A1A1 genotype is the square of the frequency of allele A1, which is 0.9^2 = 0.81.

Question 20

In a Hardy-Weinberg population with two alleles A1 and A2 that are in equilibrium, the frequency of allele A2 is 0.2. What is the frequency of individuals that are heterozygous for this allele?

Accepted Answer

The frequency of allele A2 is given as 0.2, so the frequency of allele A1 is 1 - 0.2 = 0.8. The frequency of heterozygous individuals (A1A2) can be calculated using the formula 2pq, where p is the frequency of one allele (A1) and q is the frequency of the other allele (A2). Therefore, 2 * 0.8 * 0.2 = 0.32.

Quiz 23: Microevolution