Directional artificial selection favoring the AdhF allele in experimental Drosophila populations.

 The AdhF allele increases in frequency in both of the experimental populations exposed to an ethanol-rich environment. Allele frequencies in the two control populations (no natural selection) drift up and down over the generations, ending up higher (control 1) and lower (control 2) than their starting frequencies The AdhF allele increases in frequency in both of the experimental populations exposed to an ethanol-rich environment. Allele frequencies in the two control populations (no natural selection) drift up and down over the generations, ending up higher (control 1) and lower (control 2) than their starting frequencies

Frequency of Ath 1.0 0.8 20 30 Generation Population 1 Population 2 Control 1 Control 2 40 50 High-ethanol environment Zero-ethanol environment