Name
Date
AP: CHAPTER 23B
THE EVOLUTION OF POPULATIONS
1. Suppose that in order to establish a breeding flock of chickens, you purchased 20 birds with normal feathers
and 30 birds with “frizzled” feathers. The gene controlling feather type has two alleles, MN and MF. The
MNMN homozygotes have normal feather, MFMF homozygotes have frizzled feathers, and heterozygotes
have intermediate plumage.
After allowing these chickens to interbreed, you count the number of normal, intermediate, and frizzled
individuals among their offspring.
a. If Hardy-Weinberg equilibrium were attained, what allele frequencies and genotypic frequencies would
be expected among these offspring?
Allele
MF
MN
Frequency
Genotype
MFMF
MNMF
MNMN
Frequency
b. Suppose that the offspring actually produced by starter flock consisted of 32 normal, 86 intermediate,
and 32 frizzled birds. Find the allele frequencies and genotypic frequencies.
Allele
MF
MN
Frequency
Genotype
MFMF
MNMF
MNMN
Frequency
c. Propose a hypothesis that might account for the difference between the observed frequencies and those
expected had the population attained genetic equilibrium.
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2. Phenylketonuria, described on page 457 of your text, is inherited as an autosomal recessive. About 1 in
every 10,000 newborn Caucasian infants is affected by this condition. If this population is in HardyWeinberg equilibrium, what percentage of the population are carriers (heterozygotes)?
3. Among African-Americans, the frequency of sickle-cell anemia (which, as you will recall, is a homozygous
recessive condition) is about 0.0025. What is the frequency of the heterozygote?
When 1 African-American marries another, what is the probability that both will be heterozygous?
If both are heterozygotes, what is the probability that their 1st child will have sickle-cell anemia?
4. Given q2 = .49, q = .7, p = .3, p2 = .09, 2pq = .42
a. Using the punnett square below, show that the next generation of the population will have exactly the
same composition, assuming Hardy-Weinberg equilibrium.
(
)T
(
)t
(
)T
(
) TT
(
)Tt
(
)t
(
) Tt
(
) tt
b. The frequency of T =
c. The frequency of t =
d. Describe the gene pool of the next generation.
e. What does this prove?
f. How do we know when evolution occurs?
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5. Label each statement as one of the following agents of evolutionary change:
gene flow
genetic drift mutations
natural selection
nonrandom mating
a.
Investigators have discovered that multiple alleles are common in a
population.
b.
Populations are subject to a new allele entering due to migration of
organisms between populations.
c.
Female birds of paradise choose mates with the most splendid
feathers.
d.
Investigators discovered that if they randomly picked out a few flies
from each to start the next generation, gene pool frequency changes
appeared.
e.
Giraffes with longer necks get a larger share of resources and tend to
have more offspring
6. Match these descriptions to one of the agents of evolutionary change listed in question 5. (Some agents are
used more than once.)
a.
Dwarfism is common among the Amish of Lancaster County,
Pennsylvania.
b.
Cheetahs are homozygous for a larger proportion of their genes.
c.
This agent of change tends to make the members of a population
dissimilar to one another.
d.
This agent of change tends to make the members of a population
similar to one another.
e.
Bacteria and insects become resistant to agents that formerly killed
them.
7. How does genetic drift apply to each of the following? Give an example of each.
a. Founders effect
b. Bottleneck effect
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8. How do each of the following break H-W assumptions?
a. Natural Selection:
b. gene flow
c. Mutation
d. selective mating
9. Match the observations to the correct type of natural selection at work:
directional
disruptive
stabilizing
a.
Trees in a windy area tend to remain the same size each year.
b.
The brain size of hominids steadily increases.
c.
Individuals from the same moth species tend to have blue stripes in open
areas and orange stripes in forested areas.
10. Match the types of natural selection listed in question 9 with the following diagrams:
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11. Evolution is one of the unifying themes of biology. Evolution involves change in the frequencies of alleles
in a population. For a particular locus in a population, the frequency of the recessive allele (a) is 0.4 and
the frequency of the dominant allele (A) is 0.6.
(a) What is the frequency of each genotype (AA, Aa,aa) in this population? What is the frequency of the
dominant phenotype?
(b) How can the Hardy-Weinberg principle of genetic equilibrium be used to determine whether this
population is evolving?
(c) Identify a particular environmental change and describe how it might alter allelic frequencies in this
population. Explain which condition of Hardy-Weinberg principle would not be met.
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