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Chapter 5: Population Genetic
Chapter Review
5.1 Gene Pool Concept
Explain gene pool and allele frequency
Explain population genetics and its relation to
allele frequency
Explain allele frequency and genetic
equilibrium
Describe the changes in allele frequency
5.2 Hardy-Weinberg Law
State the Hardy-Weinberg Law
Explain five assumptions of Hardy-Weinberg
Law for genetic equilibrium.
Using the Hardy-Weinberg equations to
calculate alleles and genotype frequencies.
Extra Exercise
Multiple Choice Question
1. A population is defined as __________.
a. members of the same species, living in the same area, that have the potential
to interbreed
b. members of the same genus, living in the same area, that have the potential to
interbreed
c. interbreeding members of the same species
d. members of the same species
e. members of the same genus
2. Which of the following is NOT a condition of the Hardy-Weinberg law?
a. Mating within the population occurs at random with respect to the loci under
consideration.
b. The population is infinitely large or, in practical terms, is large enough that
sampling errors and random effects are negligible.
c. No more than one other factor—mutation, migration, or random genetic
drift—can be acting at one time during the period under study.
d. There is no selective advantage for any of the genotypes under consideration;
all genotypes are equally viable and fertile.
e. All of the above are conditions of the Hardy-Weinberg law.
3. All members of an isolated village were genotyped for a particular RFLP. Of the
1000 individuals, 200 were homozygous for the presence of the restriction site, 700
were heterozygous, and 100 were homozygous for its absence. What is the frequency
of the "restriction site present" allele, p?
a.
b.
c.
d.
e.
0.55
0.45
0.9
0.2
None of the above
4. If an autosomal recessive disorder which shows Hardy-Weinberg equilibrium has an
incidence of 1 in 6400 then the frequency of carriers is approximately _______.
a. 1 in 20
b. 1 in 40
c. 1 in 80
d. 1 in 160
e. 1 in 120
5. If an X-linked recessive disorder is in Hardy-Weinberg equilibrium and the incidence
in males equals 1 in 100, then the expected incidence of affected homozygous
females would be _______.
a. 1 in 1000
b. 1 in 4000
c. 1 in 10000
d. 1 in 40000
Short Answer:
1. What conditions must be meet for a population to be in Hardy-Weinberg Equilibrium?
2. Explain why population size is important to the Hardy-Weinberg Law.
3. What must be true of mating within a population for it to be in Hardy-Weinberg
equilibrium?
4. What characterizes a population in Hardy-Weinberg equilibrium?
Genetic Problem:
1. In a population of giraffes, the gene that determines spot size has two alleles, S for
larger spots and s for smaller spots. Giraffes with one of each allele have mediumsized spots. In one generation, the frequency of S is p=0.4 and the frequency of s is
q=0.6. Since spots help the giraffes blend in with their surroundings, they are acted
upon by natural selection. In the next generation, 64% of giraffes have small spots.
What percentage of giraffes in the second generation will have medium spots? Large
spots?
2. Your original population of 200 was hit by a tidal wave and 100 organisms were
wiped out, leaving 36 homozygous recessive out of the 100 survivors. If we assume
that all individuals were equally likely to be wiped out, how did the tidal wave affect
the predicted frequencies of the alleles in the population? NOTE: assume the new
population is at equilibrium -- AFTER the event - so you are comparing two
populations what are at equilibrium to look for changes in allele frequencies.
a. What is the frequency of homozygous recessive?
b. What is the predicted frequency of heterozygotes?
c. What is the predicted frequency of homozygous dominant?
3. Lets say that brown fur coloring is dominant to gray fur coloring in mice. If
you have 168 brown mice in a population of 200 mice........
a. What is the predicted frequency of heterozygotes?
b. What is the predicted frequency of homozygous dominant?
c. What is the predicted frequency of homozygous recessive?
4. If 81% of a population is homozygous recessive for a given trait..........
a. What is the predicted frequency of homozygous dominant?
b. What is the predicted frequency of heterozygotes?
c. What is the frequency of the dominant and recessive alleles in the
population?
5. If 51% of the population carries at least one copy of the recessive allele.......
a. What is the predicted frequency of individuals in the population that
express the dominant phenotype?
b. What is the predicted frequency of individuals in the population that
express the recessive phenotype?
6. You have sampled a population in which you know that the percentage of the
homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the
following:
a.
b.
c.
d.
e.
The frequency of the "aa" genotype.
The frequency of the "a" allele.
The frequency of the "A" allele.
The frequencies of the genotypes "AA" and "Aa."
The frequencies of the two possible phenotypes if "A" is completely
dominant over "a."
7. Within a population of butterflies, the color brown (B) is dominant over the
color white (b). And, 40% of all butterflies are white. Given this simple
information, which is something that is very likely to be on an exam, calculate
the following:
a. The percentage of butterflies in the population that are heterozygous.
b. The frequency of homozygous dominant individuals.
8. A rather large population of Biology instructors have 396 red-sided
individuals and 557 tan-sided individuals. Assume that red is totally recessive.
Please calculate the following:
a. The allele frequencies of each allele.
b. The expected genotype frequencies.
c. The number of heterozygous individuals that you would predict to be
in this population.
d. The expected phenotype frequencies.
e. Conditions happen to be really good this year for breeding and next
year there are 1,245 young "potential" Biology instructors. Assuming
that all of the Hardy-Weinberg conditions are met, how many of these
would you expect to be red-sided and how many tan-sided?
9. A very large population of randomly-mating laboratory mice contains 35%
white mice. White coloring is caused by the double recessive genotype, "aa".
Calculate allelic and genotypic frequencies for this population.
10. Cystic fibrosis is a recessive condition that affects about 1 in 2,500 babies in
the Caucasian population of the United States. Please calculate the following.
a. The frequency of the recessive allele in the population.
b. The frequency of the dominant allele in the population.
c. The percentage of heterozygous individuals (carriers) in the population.
11. The ability to taste PTC is due to a single dominate allele "T". You sampled
215 individuals in biology, and determined that 150 could detect the bitter
taste of PTC and 65 could not. Calculate all of the potential frequencies.