(A) The allele frequencies changed because the removal of individuals from small populations is

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1 1. Sandpipers are medium-sized shorebirds. The table below shows population and phenotypic data for a sandpiper population on a barrier island in 2009 and in The island was hit by a large hurricane in Assuming that all individuals were equally likely to die as a result of the hurricane, and that the population was in Hardy-Weinberg equilibrium before the hurricane, which statement best explains why the allele frequencies changed after the hurricane? (A) The allele frequencies changed because the removal of individuals from small populations is more likely to result in altered allele frequencies. This answer suggests the student understands that the allele frequencies were affected by the hurricane because the population is small and small populations are more susceptible to changes in allele frequencies (due to genetic drift) than large populations. (B) The allele frequencies changed because individuals are more likely to engage in random mating after a rapid population decline. This answer suggests the student may understand that random mating is a condition for a population to be in Hardy-Weinberg equilibrium, but does not understand that there is no evidence to support that the sandpipers practiced nonrandom mating before the hurricane, or that the allele frequencies changed as a result of the small population size, which is more susceptible to allele frequency changes (due to genetic drift). (C) The allele frequencies changed because environmental stresses increase the rate of genetic mutations, which cause harmful alleles to appear more frequently. Page 1 of 5

2 This answer suggests the student may understand that in order to be in Hardy-Weinberg equilibrium, a population cannot have mutations, but does not understand that the rate at which mutations occur does not increase in response to environmental stresses, or that the allele frequencies changed as a result of the small population size, which is more susceptible to allele frequency changes (due to genetic drift). (D) The allele frequencies changed because natural disasters often result in a shift in allele frequencies as a result of gene flow. This answer suggests the student may understand that gene flow can be a factor in changing allele frequencies within a population, but does not understand that gene flow is caused by the immigration of new individuals, which is not supported by the data in the table, or that the allele frequencies changed as a result of a small population size, which is more susceptible to allele frequency changes (due to genetic drift). 2. In a population of squirrels in Hardy-Weinberg equilibrium, the allele for black fur (g) is recessive to the allele for gray fur (G). Approximately 9% of the squirrels have black fur and 42% of the squirrels with gray fur carry the black allele. What are the frequencies for the black allele and the gray allele in this population? (A) Black allele = 0.09; gray allele = 0.91 This answer suggests the student may understand that 9% of the population has the recessive phenotype and 91% has the dominant phenotype (at least one copy of the G allele), but does not understand that 9% represents the squirrels with the recessive phenotype (q 2 ), not the allelic frequency of q. (B) Black allele = 0.30; gray allele = 0.70 This answer suggests the student understands which formula can be used to calculate allelic frequencies (p and q) given phenotypic information, and understands that squirrels with the recessive phenotype represent q 2, and that once q is determined, p can be determined by subtracting q from 1. Page 2 of 5

3 (C) Black allele = 0.58; gray allele = 0.42 This answer suggests the student may understand that 42% of the squirrels with gray fur are homozygous and carry the black allele (genotypic frequency), but does not understand that this is not the same thing as the allelic frequency within a population, or that the data for homozygous recessive black squirrels should be used to determine q 2. (D) Black allele = 0.81; gray allele = 0.19 This answer suggests the student may understand that 9% represents the recessive allele and that the sum of both alleles must be 1, but does not understand that 9% represents q 2 and not q. 3. In a population that is in Hardy-Weinberg equilibrium, there are two alleles for freckles. The allele for having freckles (F) is dominant to the allele for not having freckles (f). If 12% of the population does not have freckles, what is the frequency of the allele for having freckles? (A) 0.35 (B) 0.45 (C) 0.65 This answer suggests the student may understand how to calculate the allelic frequency of q, but does not understand that q is the recessive allele or that the frequency of the dominant allele is 1 q. This answer suggests the student may understand how to calculate 2pq given the percent of the population with the recessive phenotype (q 2 ), but does not understand that the recessive genotypic frequency represents q 2 and that it should be used to determine the allele frequency of q. Page 3 of 5

4 This answer suggests the student understands how to convert genotypic data into allelic frequencies and calculates the correct frequency for the dominant allele (p) given the recessive genotypic frequency (q 2 ). (D) 0.88 This answer suggests the student may understand that 84% of the population has freckles by computing p 2 + 2pq, but does not understand that this represents the dominant phenotypic frequency and not the dominant allelic frequency. 4. In fruit flies (D. melanogaster), the frequency of the allele (r) that confers resistance to DDT, an insecticide, was found to be 0% in 1930 when the poison was first introduced. By the late 1960s, the frequency of the r allele had risen to 37%. DDT was banned in the United States by the early 1970s. In a small population of fruit flies, approximately 19% of fruit flies are homozygous for the r allele and 49% are heterozygous. Based on this information, which statement best explains what has happened to the frequency of the r allele in this population since the late 1960s? (A) The r allele frequency has increased from 0.37 to 0.81, which indicates that flies with resistance to the pesticide are able to outcompete flies without resistance. This answer suggests the student may understand that an increase in the frequency of a recessive allele would indicate a selective advantage, but does not understand that the square root of the homozygous recessive genotype (rr) is taken to find the allelic frequency of the resistance allele (q). (B) The r allele frequency has increased from 0.37 to 0.49, which indicates a selective disadvantage for individuals who do not carry the r allele. This answer suggests the student may understand that an increase in an allelic frequency may indicate a selective advantage, but confuses allelic frequency with genotypic frequency and does not understand that a rise in the frequency of a recessive allele does not mean that there is a selective disadvantage for individuals who carry the dominant allele. Page 4 of 5

5 (C) The r allele frequency has increased from 0.37 to 0.44, which indicates that the r allele still provides some sort of selective advantage. This answer suggests the student understands how to calculate allelic frequency data from genotypic data, and that the r allele frequency has most likely increased since the 1960s based on the small sample population, which indicates that flies that carry the r allele have some sort of selective advantage over flies that do not carry the r allele. (D) The r allele frequency has increased from 0.37 to 0.68, which indicates that the allele still provides for increased survival and therefore remains in the gene pool. This answer suggests the student may understand that an increase in the frequency of the r allele indicates that it still carries a selective advantage over the R allele, and that 68% of the population carries the r allele, but does not understand that this represents the genotypic frequency and not the allelic frequency for the r allele. Page 5 of 5