CHAPTER 23 STUDY GUIDE: THE EVOLUTION
OF POPULATIONS
KEY WORDS
Biochemistry
gene flow
Molecular Genetics
bottleneck effect
Modern Synthesis
founder effect
species
selection pressure
gene pool
polymorphism
allelic frequency
heterozygote advantage
genetic equilibrium
directional selection
genotype frequencies
disruptive selection
Hardy-Weinberg Law
stabilizing selection
genetic drift
balanced polymorphism
neutral selection
sexual selection
mutation pressure
WORD ROOTS
inter - = between (intersexual selection: individuals of one sex are choosy in selecting their mates
from individuals of the other sex, also called mate choice)
intra - = within (intrasexual selection: a direct competition among individuals of one sex for mates
of the opposite sex)
micro - = small (microevolution: a change in the gene pool of a population over a succession of
generations)
muta - = change (mutation: a change in the DNA of genes that ultimately creates genetic
diversity)
poly - = many; morph - = form (polymorphism: the coexistence of to or more distinct forms of
individuals in the same population)
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QUESTIONS
1. Explain the concept of the gene pool.
2. In a population of 200 mice, 98 are homozygous dominant for brown color
(BB), 84 are heterozygous (Bb), and 18 are homozygous recessive (bb).
a. The allele frequencies of this population are:
___________ B allele
___________ b allele
b. The genotype frequencies of this population are:
______ BB
______ Bb
______ bb
3. Use the allele frequencies you determined in question 2 to predict the
genotype frequencies of the next generation:
Frequencies of:
B(p) = _______
BB = p2 = _______
b(q) = ________
Bb = 2pq = _______
bb = q2 = _______
4. State the Hardy-Weinberg Law, and discuss its four conditions for
maintenance of genetic equilibrium. Why are these conditions rarely met
in nature?
5. Practice using the Hardy-Weinberg equation so that you can easily
determine genotype frequencies from the allele frequencies and vice
versa.
a. The allele frequencies in a population A = 0.6 and a = 0.4.
Predict the genotype frequencies for the next generation:
AA _____
Aa _____
aa _____
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b. What would the allele frequencies be for the generation you
predicted above in part a.?
A _________
a _________
c. Suppose that one gene locus determines stripe pattern in
skunks. SS skunks have two broad stripes; Ss skunks have two
narrow stripes; ss skunks have white speckles down their backs. A
sampling of a population of skunks found 65 broad-striped skunks,
14 narrow-striped skunks, and 1 speckled. Determine the allele
frequencies:
S _________
s _________
6. Explain how natural selection in one generation can affect the genotype of
the next generation.
7. Using diagrams contrast directional selection, stabilizing selection and
disruptive selection.
8. Contrast the roles of selection and mutation in directing evolutionary
change.
9. Explain how a characteristic can have both positive and negative effects
and indicate what determines whether or not a trait will increase or
decrease in a population.
10. Describe heterozygote superiority, explain how this process helps
maintain deleterious recessive genes. (Note sickle cell anemia)
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