Question 1

Which of the following is an assumption of the Hardy-Weinberg model?

Accepted Answer

The Hardy-Weinberg model assumes random mating with respect to genotype, meaning individuals pair by chance, not by genotype.

Question 2

The figure shows the allele frequency trajectories for two populations starting from two different initial frequencies. Which evolutionary processes could produce this result?

Accepted Answer

A

Question 3

Pocket mice have light- or dark-colored coats and live in dark- or light-colored habitats. Pocket mice whose coat colors match their environment are less susceptible to predation. In the scenarios shown in the figure, which of the following selection coefficients might you expect (on each genotype in each habitat)? A

B

C

D

Accepted Answer

B

Question 4

A sample of 2,000 individuals from a human population was scored for MN blood group. The following frequencies were found: 1,600 MM, 250 MN, and 150 NN. How do these numbers compare to those expected under Hardy-Weinberg equilibrium?

Accepted Answer

The observed frequencies of MM (1600/2000 = 0.8), MN (250/2000 = 0.125), and NN (150/2000 = 0.075) do not match the Hardy-Weinberg equilibrium expectations, which would predict genotype frequencies based on allele frequencies. The allele frequency for M can be calculated as (2*1600 + 250)/(2*2000) = 0.825, and for N as (2*150 + 250)/(2*2000) = 0.175. Under Hardy-Weinberg, the expected frequency of MN heterozygotes would be 2pq = 2*(0.825)*(0.175) = 0.2885, which is significantly higher than the observed 0.125, indicating there are fewer MN heterozygotes than expected.

Question 5

What kind of equilibrium does overdominance produce?

Accepted Answer

Overdominance results in a stable equilibrium, as selection favors heterozygous individuals with both alleles, maintaining genetic diversity within a population.

Question 6

Stalk height in sunflowers is determined by two alleles at a locus, T and t, which display incomplete dominance. TT individuals are tall, Tt are medium, and tt are short. In a population that is in Hardy-Weinberg equilibrium, we count 1,546 short plants out of 9,666. How many plants do you expect to be tall?

Accepted Answer

We can use the Hardy-Weinberg equation to solve the problem:
p^2 + 2pq + q^2 = 1
where p is the frequency of the T allele and q is the frequency of the t allele in the population.
From the problem, we know that:
q^2 = 1,546/9,666 
q^2 = 0.160
q = 0.4 (because this is a case of incomplete dominance, we cannot assume q is equal to 0.2)
Using the fact that p + q = 1 and q = 0.4, we can find that p = 0.6.
To find the expected frequency of tall plants, we can use the equation:
p^2 = (0.6)^2 = 0.36
Finally, we can multiple the expected frequency by the total number of plants:
0.36 x 9,666 = 3,480
Therefore, the answer is C) 3,480.

Question 7

Natural selection can act on both ________, which is the probability of survival, and ________, which is the number of offspring produced.

Accepted Answer

Natural selection can act on the viability, or probability of survival, of individuals in a population as well as their fecundity, or the number of offspring they produce. This is because individuals who are more likely to survive and produce more offspring will pass on more of their advantageous traits to the next generation, leading to changes in the overall characteristics of the population over time. Epistasis and epigenetics are not directly related to natural selection, while directional selection and frequency-dependent selection are specific types of natural selection rather than the general concepts of viability and fecundity. Livelihood and income are also not relevant to natural selection.

Question 8

The table shows the survival and seed production of hybrid and wild sunflowers at three different sites. What do these data demonstrate?

Accepted Answer

The data shows that the hybrid plants have lower seed production compared to wild plants, indicating reduced fecundity. However, the survival rates of hybrid and wild plants are similar, indicating similar viability. Therefore, the best choice is A, which states that the hybrid plants experience reduced fecundity but similar viability to wild plants. Choices B, C, and D are not supported by the data.

Question 9

Consider a locus with two alleles, A and a. Under which of the following scenarios will the frequency of the A allele increase?

Accepted Answer

In scenario A, individuals with the A allele have a higher fitness, meaning they are more likely to survive and reproduce. As a result, the frequency of the A allele will increase in the population over time. In scenarios B and C, heterozygotes either have higher or lower fitness than both homozygotes, which can lead to different outcomes depending on the specific conditions. In scenario D, the aa individuals have higher fitness, which means they are more likely to survive and reproduce. This would lead to a decrease in the frequency of the A allele in the population over time.

Question 10

Consider two events that are mutually exclusive, that is, if one occurs, the other cannot occur. The probability that either one will occur is ________, and the probability that both will occur is ________.

Accepted Answer

The probability that either of two mutually exclusive events will occur is the sum of their individual probabilities, and the probability that both will occur is zero, since mutually exclusive events cannot happen together.

Question 11

The figure shows the change in allele frequencies over many generations. What differs between the populations represented by the three colors?

Accepted Answer

The answer of The figure shows the change in allele...

Question 12

Consider a population that is in Hardy-Weinberg equilibrium at a locus with two alleles, A and a, at frequencies of p and q, respectively. Assuming the population remains in Hardy-Weinberg equilibrium, what is the expected frequency of Aa heterozygotes after 100 generations?

Accepted Answer

According to Hardy-Weinberg equilibrium, the frequency of Aa heterozygotes can be calculated using the formula 2pq, where p and q are the frequencies of the A and a alleles, respectively. Since the population is in equilibrium, the frequencies will remain constant over time, so the expected frequency of Aa heterozygotes after 100 generations is still 2pq.

Question 13

Which of the following genotypic fitness values would result in the most rapid fixation of the beneficial allele, A?

Accepted Answer

In order for a beneficial allele to fix rapidly (i.e. reach a frequency of 1 in the population), it needs to provide a significant fitness advantage over the alternative allele. In this case, option B has the largest fitness difference between the homozygous dominant and heterozygous genotypes (0.1 difference), while still maintaining a solid fitness advantage for the beneficial allele over the recessive allele (0.2 difference). This larger fitness difference will result in faster selection for the beneficial allele and faster fixation in the population.

Question 14

Population sex ratios, that is, how many males and females there are in a population, are most likely influenced by which process?

Accepted Answer

Frequency-dependent selection can influence population sex ratios because it refers to an evolutionary process where the fitness of a phenotype depends on its frequency relative to other phenotypes in a given population. This can lead to changes in sex ratios if, for example, one sex becomes too common and the opposite sex thus becomes more valuable for reproductive success.

Question 15

Proponents of eugenics sought to eliminate alleles for so-called undesirable traits by not allowing people with those traits to reproduce. Which of the following scenarios would prevent the elimination of these alleles?

Accepted Answer

Undesirable traits caused by rare, recessive alleles would not be eliminated simply by preventing individuals with those traits from reproducing because carriers of the recessive allele (who do not express the trait) could still pass the allele to their offspring.

Question 16

What type of selection is demonstrated in the figure shown?

Accepted Answer

The answer of What type of selection is demonstrated in...

Question 17

The null model for population genetics is

Accepted Answer

The null model for population genetics is the Hardy-Weinberg model, which provides a theoretical framework for understanding the genetic structure of populations over time. This model assumes that a population is at equilibrium with respect to allele frequencies and genotypic frequencies, in the absence of forces such as mutation, migration, genetic drift or natural selection. This model forms the foundation of much of population genetics theory and research.

Question 18

Why do you need to use a statistical test (e.g., the chi-square test) to compare the observed genotype frequencies in a population to those expected under Hardy-Weinberg equilibrium?

Accepted Answer

A statistical test is necessary to assess the probability that the deviation of observed genotype frequencies from those expected under Hardy-Weinberg equilibrium occurred due to chance. This helps to distinguish between natural selection and other factors that could cause a population to deviate from equilibrium. Option B is incorrect as the observed genotype frequencies can be determined through sampling. Option D is incorrect as the frequencies expected under Hardy-Weinberg equilibrium are accurate if the assumptions of the model are met.

Question 19

Mathematical descriptions of evolutionary processes allow biologists to make ________ predictions about how genotype frequencies change over time.

Accepted Answer

Mathematical descriptions of evolutionary processes allow biologists to make quantitative predictions about how genotype frequencies change over time.

Question 20

Which of the following would best help you predict the fate of an allele in a population?

Accepted Answer

Determining survival rates of individuals of each genotype helps predict the fate of an allele because it provides information on natural selection pressures affecting the allele's frequency in the population.

Quiz 7: The Genetics of Populations