The table provides information on two populations, Population 1 on the left and Population 2 on the right, in 2 years, 1980 and 2010. The first row has column headers from left to right: Year, Allele uppercase R and Allele lowercase r for Population 1, and Allele uppercase R and Allele lowercase r for Population 2. The data in the next two rows are as follows, from left to right: Row 2: 1980, Population 1: Allele uppercase R, 0.3; Allele lowercase r, 0.7. Population 2: Allele uppercase R, 0.37; Allele lowercase r, 0.63. Row 3: 2010, Population 1: Allele uppercase R, 0.0; Allele lowercase r, 1.0. Population 2: Allele uppercase R, 0.75; Allele lowercase r, 0.25.

The table shows the changes in allele frequencies of a specific gene in two populations of randomly mating small mammals after 30 years. The populations inhabit adjacent equatorial islands that have similar topography and climate. Which of the following is the most reliable conclusion that can be drawn from analysis of the data above?

Question

The table provides information on two populations, Population 1 on the left and Population 2 on the right, in 2 years, 1980 and 2010. The first row has column headers from left to right: Year, Allele uppercase R and Allele lowercase r for Population 1, and Allele uppercase R and Allele lowercase r for Population 2. The data in the next two rows are as follows, from left to right: Row 2: 1980, Population 1: Allele uppercase R, 0.3; Allele lowercase r, 0.7. Population 2: Allele uppercase R, 0.37; Allele lowercase r, 0.63. Row 3: 2010, Population 1: Allele uppercase R, 0.0; Allele lowercase r, 1.0. Population 2: Allele uppercase R, 0.75; Allele lowercase r, 0.25.

The table shows the changes in allele frequencies of a specific gene in two populations of randomly mating small mammals after 30 years. The populations inhabit adjacent equatorial islands that have similar topography and climate. Which of the following is the most reliable conclusion that can be drawn from analysis of the data above?

BlackTom AI · Accepted Answer

Restating the question and options: The prompt provides allele frequency data for Population 1 (P1) and Population 2 (P2) in 1980 and 2010 for alleles R (uppercase) and r (lowercase). In 1980, P1 has R = 0.3 and r = 0.7, while P2 has R = 0.37 and r = 0.63. In 2010, P1 has R = 0.0 and r = 1.0, while P2 has R = 0.75 and r = 0.25. The question asks which conclusion is most reliable from analyzing these data. The answer choices are: 1) Genetic drift has occurred in population 1. 2) Population 2 is in Hardy-Weinberg equilibrium. 3) Selection for allele r is occurring in both populations. 4) The reduced frequency of allele R in population 1 will eventually lead to the extinction of population 1.

Option 1 analysis: Genetic drift has occurred in population 1. The data show that P1’s allele frequencies shifted dramatically from 0.3 (R) and 0.7 (r) in 1980 to 0.0 (R) and 1.0 (r) in 2010, despite the populations living on neighboring islands with similar environments. In small, randomly mating populations, genetic drift can cause allele frequencies to fluctuate widely from one generation to the next, potentially fixing one allele (R or r) and reducing heterogeneity. The fixation of allele r in P1 over 30 years is consistent with drift in a small population, particularly since there is no information about strong selective pressures uniquely favoring R or r in P1 that would explain a rapid, directional fixation via selection. Thus, this option aligns with drift as a plausible explanation.

Option 2 analysis: Population 2 is in Hardy-Weinberg equilibrium. The Hardy-Weinberg principle describes a population with random mating and no evolutionary forces acting (no migration, mutation, selection, or drift) and expects genotype frequencies to remain constant and allele frequencies to predict genotype frequencies. The data provided only give allele frequencies (R and r) for P2 in 1980 and 2010, not genotype frequencies (RR, Rr, rr). Even if allele frequencies changed, that alone does not confirm Hardy-Weinberg equilibrium; more information on genotype frequencies and mating structure is required. Moreover, P2 shows a substantial shift in allele frequencies from 0.37/0.63 to 0.75/0.25, which would not be expected under a strict Hardy-Weinberg scenario without a countervailing force. Therefore, concluding Hardy-Weinberg equilibrium for P2 is not justified based on the provided data.

Option 3 analysis: Selection for allele r is occurring in both populations. If selection favored allele r specifically, we would expect allelic shifts toward r in both populations, or at least a consistent pattern across them. However, in P2, r decreases from 0.63 to 0.25, which actually indicates selection favoring R, not r. In P1, r increases to fixation (r = 1.0), which could be due to drift or strong selection for r, but the data do not show a parallel selection pattern in both populations. Since one population appears to be moving toward r due to possible drift and the other toward R due to an opposite force, there isn’t a uniform selective trend for r in both populations. This makes the assertion of selection for r in both populations unsupported by the data.

Option 4 analysis: The reduced frequency of allele R in population 1 will eventually lead to the extinction of population 1. While fixation of a single allele in a small population can reduce genetic diversity and elevate extinction risk in some contexts, concluding that the population will go extinct solely from the observed allele frequency change is an overreach. Extinction likelihood depends on many factors beyond a single-locus allele frequency change, including overall fitness effects, demographic stability, environmental variation, and genetic load. The data do not provide a direct link to extinction risk for P1, only a note that R has been lost in P1 by 2010. Therefore, predicting extinction from this observation alone is not warranted.

APBIO142-030 with labs S23 - CollegeBoard* AP Exam Prep: Multiple Choice

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