BCOR 102 Exam 2
3/15/06
Name:
1. A population has three alleles (A, B, and C) at a particular locus. The frequency
of the A allele is 0.1, the frequency of the B allele is 0.2 and the frequency of the
C allele is 0.7. Assume the population is in Hardy-Weinberg equilibrium.
a. What is the probability of finding a CC homozygote?
b. What is the probability of finding an BC heterozygote?
2. You have two populations of minnows in two adjacent ponds separated by a small
dam. Population 1 has 1000 fish and the frequency of allele A is p=0.5.
Population 2 has only 500 fish, all “AA” homozygotes. After the dam fails, the
two populations become completely mixed. What will be the new allele
frequency in the combined population of 1500 fish?
3. An ecologist studying the flower color of lupines finds 200 red-flowered plants,
50 pink-flowered plants and 100 white-flowered plants, which represent the three
genotypes at one locus: RR and Rr and rr. Use a chi-square test to determine if
the population is in Hardy-Weinberg equilibrium (Note: the critical value of X2
for this test is 3.84)
4. The following genotypes were observed at the enzyme locus PGM in the
flowering plant Impatiens capensis. Three different patterns were observed when
150 different individuals were analyzed by gel electrophoresis. The results are
summarized in the following figure.
N=
70
30
50
(The numbers above each column are
the number of individuals that had that
------particular banding pattern.)
------a. What is the observed
heterozygosity for this
population?
b. What is the expected
heterozygosity under HWE?
c. What is the inbreeding coefficient (F)?
d. What biological process could account for that pattern of heterozygosity?
5. A population is in Hardy-Weinberg equilibrium with two alleles at the “A” locus.
The three genotypes have the following frequencies and relative fitnesses.
AA
Aa
aa
Frequency
0.09 0.42 0.49
Relative fitness
1
0.8
0.6
a. What is the starting frequency of of allele “A”?
b. What will be the frequency of the A allele next generation?
6. Mosquitoes with a dominant R allele have increased resistance to the pesticide
DDT. Homozygous recessive rr mosquitoes have 60% lower survival. Initially
the frequency of the R allele in the population is p=0.20. What is the expected
frequency of R after one generation of selection by DDT?
7. Populations of the alpine sky pilot have different flower sizes in different
locations. Tundra populations have larger flowers than meadow populations.
a. How could you tell if those differences are genetic in origin, or if the
difference is simply the result of growing in a different habitat?
b. How could you measure the heritability of flower size?
8. Fill out the following table showing the effects of each evolutionary process on
allele frequency: (increase or decrease or neither or both)
Effect on
Effect on
Affects all loci
Process
variation within a variation between equally? (Y/N)
population?
populations?
Migration
Mutation
Drift
Selection
9. The following data were observed for populations of Daphnia pulex. FSTwas used
to measure pattern of differentiation among populations for 5 different enzyme
loci.
Enzyme FST
Adh
0.03
Est
0.01
Idh
0.03
Gpi
0.22
Pgm
0.02
a. Is it more likely that selection or drift produced that pattern? Explain.
10. A population geneticist studying populations of grizzly bears in the Canadian
Rockies analyzed the pattern of variation at several loci. She found that the
average FST among northern populations was 0.04 and the average FST among
southern populations of grizzly’s was 0.23.
a. Which set of populations (northern or southern) had more similar allele
frequencies?
b. Which set of populations has a higher migration rate?
c. Bonus: what is the predicted number of migrants (Nm) per generation in
the northern populations?
11. In a classic study of natural selection, Bumpus (1917) found a population of
sparrows that had washed up on a beach after a particular severe fall storm. Some
of the birds were still alive and some were dead. The overall average body length
of the entire population was 159.5 mm, which was presumably a good estimate of
the entire population before the storm. The average body length of the surviving
birds was 158.7 mm and the average body length of dead birds was 160.4 mm. If
the heritability of body length is 0.3, was
was the predicted length for this population
in the next generation?
12. Buri studied genetic drift in some
laboratory populations of fruit flies and
produced this figure of his results:
a. How would his results have differed
if the starting allele frequencies had
been 0.2 and 0.8 (instead of 0.5 and 0.5)?
b. How would his results have differed if he had used populations of 50 flies,
instead of populations of 16 flies?