The larvae of the fruit fly Drosophila melanogaster normally feedon rotting fruit, which may ferment and produce high concentrations ofalcohol. Douglas Cavener and Michael Clegg studied allelic frequenciesat the locus encoding alcohol dehydrogenase (Adh) in experimentalpopulations of D. melanogaster (D. R. Cavener and M. T. Clegg. 1981.Evolution 35:1–10). The experimental populations were establishedfrom wild-caught flies and were raised in cages in the laboratory. Twocontrol populations (C1 and C2) were raised on a standard cornmeal–molasses–agar diet. Two ethanol populations (E1 and E2) were raised ona cornmeal–molasses–agar diet to which was added 10% ethanol. Thefour populations were periodically sampled to determine the frequenciesof two alleles at the alcohol dehydrogenase locus, AdhS and AdhF. Thefrequencies of these alleles in the four populations are shown in theaccompanying graph. a. On the basis of these data, what conclusion might you draw about theevolutionary forces that are affecting the Adh alleles in these populations?b. Cavener and Clegg measured the viability of the different Adhgenotypes in the ethanol environment and obtained the following values:Genotype Relative viabilityAdhF/AdhF 0.932AdhF/AdhS 1.288AdhS/AdhS 0.596Using these relative viabilities, calculate fitnesses for the threegenotypes. If a population has an initial frequency of p = f (AdhF) = 0.5,what is the expected frequency of AdhF in the next generation in theethanol environment on the basis of these fitness values?
The larvae of the fruit fly Drosophila melanogaster normally feed
on rotting fruit, which may ferment and produce high concentrations of
alcohol. Douglas Cavener and Michael Clegg studied allelic frequencies
at the locus encoding alcohol dehydrogenase (Adh) in experimental
populations of D. melanogaster (D. R. Cavener and M. T. Clegg. 1981.
Evolution 35:1–10). The experimental populations were established
from wild-caught flies and were raised in cages in the laboratory. Two
control populations (C1 and C2) were raised on a standard cornmeal–
molasses–agar diet. Two ethanol populations (E1 and E2) were raised on
a cornmeal–molasses–agar diet to which was added 10% ethanol. The
four populations were periodically sampled to determine the frequencies
of two alleles at the alcohol dehydrogenase locus, AdhS and AdhF. The
frequencies of these alleles in the four populations are shown in the
accompanying graph.
a. On the basis of these data, what conclusion might you draw about the
evolutionary forces that are affecting the Adh alleles in these populations?
b. Cavener and Clegg measured the viability of the different Adh
genotypes in the ethanol environment and obtained the following values:
Genotype Relative viability
AdhF/AdhF 0.932
AdhF/AdhS 1.288
AdhS/AdhS 0.596
Using these relative viabilities, calculate fitnesses for the three
genotypes. If a population has an initial frequency of p = f (AdhF) = 0.5,
what is the expected frequency of AdhF in the next generation in the
ethanol environment on the basis of these fitness values?
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