Download Sandpipers are medium-sized shorebirds. The table below shows

PROCTOR VERSION
1.2 B: Hardy-Weinberg Equilibrium Quiz
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 2011. The island was hit by a
large hurricane in 2010.
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.
Rationale:
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.
Distractor Rationale:
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.
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PROCTOR VERSION
1.2 B: Hardy-Weinberg Equilibrium Quiz
Distractor Rationale:
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.
Distractor Rationale:
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).
Aligned to: LO 1.2 CA 1.2: Evaluate Hardy-Weinberg Data
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
Distractor Rationale:
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 (q2), not the allelic frequency of q.
(B) Black allele = 0.30; gray allele = 0.70
Rationale:
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 q2, and that once q is determined, p can be
determined by subtracting q from 1.
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PROCTOR VERSION
1.2 B: Hardy-Weinberg Equilibrium Quiz
(C) Black allele = 0.58; gray allele = 0.42
Distractor Rationale:
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 q2.
(D) Black allele = 0.81; gray allele = 0.19
Distractor Rationale:
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 q2
and not q.
Aligned to: LO 1.2 CA 1.2: Evaluate Hardy-Weinberg Data
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
Distractor Rationale:
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.
(B) 0.45
Distractor Rationale:
This answer suggests the student may understand how to calculate 2pq given the percent of
the population with the recessive phenotype (q2), but does not understand that the
recessive genotypic frequency represents q2 and that it should be used to determine the
allele frequency of q.
(C) 0.65
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PROCTOR VERSION
1.2 B: Hardy-Weinberg Equilibrium Quiz
Rationale:
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 (q2).
(D) 0.88
Distractor Rationale:
This answer suggests the student may understand that 84% of the population has freckles
by computing p2 + 2pq, but does not understand that this represents the dominant
phenotypic frequency and not the dominant allelic frequency.
Aligned to: LO 1.2 CA 1.2: Evaluate Hardy-Weinberg Data
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.
Distractor Rationale:
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.
Distractor Rationale:
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.
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PROCTOR VERSION
1.2 B: Hardy-Weinberg Equilibrium Quiz
(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.
Rationale:
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.
Distractor Rationale:
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.
Aligned to: LO 1.2 CA 1.2: Evaluate Hardy-Weinberg Data
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