Name: _____________________________________________________ Date: ___________ Block: _______
Population Genetics and Evolution: Lab Grade
Case Study 1: Ideal Hardy-Weinberg Population
The number of each genotype controlling the ability to taste the chemical PTC (phenylthiocarbamide) was
estimated in the table below. A bitter-taste reaction to PTC is evidence of the presence of a dominant allele in
either the homozygous condition (AA) or the heterozygous condition (Aa). The inability to taste the chemical at
all depends on the presence of the homozygous recessive allele (aa).
Generation
1
2
3
4
5
AA
8
9
9
9
7
Number of Each Genotype
Aa
17
18
19
18
18
aa
7
5
4
5
7
1. Calculate the allele frequency for the fifth generation. (Make sure to show you work)
2. Do you see a shift in the population favoring a certain genotype? Explain why?
Case Study 2: Natural Selection
In the natural environment, not all genotypes have the same rate of survival; that is, the environment might
favor some genotypes while selecting against others. An example is the human condition for sickle-cell
anemia. This is a disease caused by a mutation on one allele, and individuals who are homozygous recessive
often do not survive to reach reproductive maturity. For this case study you will assume that the homozygous
recessive individuals never survive (100% selection against), and the heterozygous and homozygous dominant
individuals survive 100% of the time.
Generation
1
2
3
4
5
AA
12
14
17
18
21
Number of Each Genotype
Aa
20
18
15
14
11
aa
0
0
0
0
0
1. Calculate the allele frequency for the fifth generation. (Make sure to show you work)
2. Predict what would happen to the frequencies of p and q if you collected data for another five generations.
3. In a large population would it be possible to completely eliminate the harmful recessive allele? Explain.
Case Study 3: Heterozygote Advantage
From Case Study 2 it is easy to see what happens to the lethal recessive allele in the population. However,
data from many human populations show an unexpectedly high frequency of sickle-cell allele in some
populations. Thus, our simulation does not accurately reflect the real situation; this is because individuals who
are heterozygous are slightly more resistant to a deadly form of malaria than homozygous dominant
individuals. In other words, there is a slight selection against homozygous dominant individuals as compared
to heterozygotes. This fact is easily incorporated in the data found below.
Generation
1
2
3
4
5
AA
9
3
6
6
4
Number of Each Genotype
Aa
15
21
18
18
4
aa
0
0
0
0
0
4. Calculate the allele frequency for the fifth generation. (Make sure to show you work)
5. Explain how the changes in p and q frequencies in Case 2 compare with Case 1 and Case 3.
6. Do you think the recessive allele will be completely eliminated in either Case 2 or Case 3? Explain why.
7. What is the importance of heterozygotes (the heterozygote advantage) in maintaining genetic variation in
populations?
Hardy-Weinberg Problems
Show all your work when solving the following problems.
8. In Drosophila the allele for normal-length wings is dominant over the allele for vestigial wings
(vestigial wings are stubby little curls that cannot be used for flight). In the population of 1,000
individuals, 360 show the recessive phenotype. How many individuals would you expect to be
homozygous dominant and heterozygous for this trait?
9. The allele for unattached earlobes is dominant over the allele for attached earlobes. In a
population of 500 individuals, 25% show the recessive phenotype. How many individuals would
you expect to be homozygous dominant and heterozygous for their trait?
10. The allele for the hair pattern called “widow’s peak” is dominant over the allele for no “widow’s
peak.” In a population of 1,000 individuals, 510 show the dominant phenotype. How many
individuals would you expect of each of the possible three genotypes for this trait?
11. In the United States about 16% of the population is Rh negative. The allele for Rh negative is
recessive to the allele for Rh positive. If the student population of a high school in the U.S. is
2,000 how many students would you expect for each of the three possible genotypes?
12. In certain African countries 4% of the newborn babies have sickle-cell anemia, which is a
recessive trait. Out of a random population of 1,000 newborns babies, how many would you
expect for each of the three possible genotypes.
13. In a certain population, the dominant phenotype of a certain trait occurs 91% of the time. What is
the frequency of the dominate allele?
14. Seventy percent of a population has the dominant trait while 30% are recessive. What percentage
of the population are carries?
15. Peas seeds can be round (R: dominant) or wrinkled (r: recessive). In a field of wild peas ninety-six
percent (96%) of the peas are round. What is the allelic frequency?
16. For foxes there exists a single gene that controls coat thickness. Allele C confers a thick coat
while allele c is a thin coat. In a certain population of 540 foxes, 49 have a thin coat. What are
the allelic frequencies?
17. In a certain population of flowers, when red and white flowers are crossed they produce pink
flowers. A certain field has 1190 red flowers, 1070 pink flowers and 240 white flowers. What is
the frequency of alleles?
18. One person in 10,000 has PKU which is a potentially lethal, recessive disorder. These individuals
lack an enzyme that allows the digestion of the main acid phenylalanine and must be careful not
to have this amino acid in their diet. What are the chances that someone is carrier, their spouse is
a carrier and then their child being a PKU victim?