Evolution 350
Problem Set #7, Semester Review.

1)  Locus A encodes a color polymorphism: A¹A¹ red, A¹A² pink, and A²A² white.  Locus B encodes production of a metabolically essential enzyme, with allele b entirely recessive and lethal.  If locus A and locus B are linked 20 map units apart, what proportion of the surviving progeny from a cross between A¹B/A²b parents are expected to be white?

2) Banded is dominant over solid shell background color in the land snail Cepaea nemoralis.  A sample of snails taken from a British meadow in the spring included 140 banded and 80 solid.  Assuming Hardy-Weinberg equilibrium, estimate the frequency of the banded gene.

3) The 220 snails were marked and returned to the meadow.  A second sample in the fall (at reproduction) returned 30 banded and 30 solids.  Assuming all mortality is due to differential thrush predation on shell color, estimate the selection coefficient and Δp.  What is the expected frequency of banded snails next generation?

4) Suppose the population of N = 60 Drosophila melanogaster inhabiting the Craig Cafeteria dumpster shows the following genotype frequencies at the alcohol dehydrogenase locus: Adh^ss = 27,   Adh^sf = 20, Adh^ff = 13.  How likely is this population in Hardy-Weinberg equilibrium?

5) Is this distribution of genotypes consistent with an inbreeding coefficient F = 0.3?  Give a value of chi square.

6) Assuming equilibrium, is the distribution of genotypes in the Craig Cafeteria fruit flies consistent with underdominance where W_ff = 0.8 and W_sf = 0.7?  Show why, no chi-square necessary.

7) Is this distribution of genotypes consistent with mutational equilibrium where mutation from the s-allele to the f-allele is 8 x 10^-4, while back mutation is 3 x 10^-5?  Show why, no chi-square necessary.

8) A second population of just N = 32 fruit flies inhabits the trash cans behind Vickery’s, with p_s = 0.97 and q_f = 0.03 at the Adh locus.  If half the flies emigrate to the Craig Cafeteria dumpster, predict the new frequency of the s-allele at Craig.

9) What is the probability that gene frequencies at the Adh locus will drift to fixation next generation in the small fly population left behind at Vickery’s?



Answers:
(1)  12%
(2) p_b = 0.397
(3) s = 0.43,  Δp = -0.085, banded phenotype = 0.527
(4) chi-square = 5.25, 0.05 > p > 0.01
(5) Yes, chi-square is negligible.
(6) No, since p_s-hat = 0.25
(7) No, since p_s-hat = 0.036
(8) p_s' = 0.691
(9) ~16%

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