Abstract
The effect of the gene-enzyme system of esterase-6 (EST-6) on the expression of viability traits in Drosophila melanogaster was studied at normal and high temperatures. Interline, ontogenetic, and sexual differences of beta-esterase activity in tissue extracts were found. The differences were not correlated with the viability parameters of the flies. Some flies in the b line, in contrast to the other lines examined (N, Canton S, cn, vg), had EST-6 forms with different electrophoretic mobility. This indicates genetic polymorphism of this line at EST-6 locus. The bS and b F lines, isogenic at the chromosome 1, 2, and 3 and homozygous for Est-6S and Est-6F, respectively, were derived from a heterozygous line b female by means of a special crossing scheme and selection. The S allozyme had lesser mobility but was more resistant to high temperature (57 degrees C). Flies from the bS line were more resistant to high temperature and were two times as fertile as the bF flies. These selective advantages of the bS line persisted for 20-45 generations at permissive high temperatures (29 degrees C). In the experimental population that started with a 1:1 ratio of Est-6S and Est-6F and was kept at 29 degrees C, an increase in the allele S frequency was demonstrated. Thus, the S allele of EST-6 can be considered as a part of the adaptational gene complex arising in population under high temperature conditions.
