PROPERTIES OF INBRED DROSOPHILA-MELANOGAS TER LINES DERIVED FROM A POPULATION SELECTED FOR AN INCREASED RATE OF EMBRYONIC-DEVELOPMENT

Two heterogeneous Drosophila melanogaster populations were subjected t o selection for an increased rate of embryonic development by picking out the first 10% of hatching larvae. After repeating this procedure i n 15 generations, ''fast'' populations were obtained, in which the dur ation of embryonic development at high temperature (31-32 degrees C) w as 30-40 min less than in nonselected control populations. The results of preliminary experiments on substituting the second and third chrom osomes in the selected and control populations provide evidence that s elected genes responsible for accelerated development are located on t he second chromosome. Inbreeding in 12 generations of selected populat ions was used to obtain about 40 lines homozygous, in particular, at t ime alcohol dehydrogenase gene. In four lines, the developmental rate was higher than in a homozygous control line, but others did nor diffe r from control or developed more slowly. The duration of embryonic dev elopment ae 32 degrees C in fast lines was 50-70 min shorter than in c ontrol, but this difference was significantly less at lower temperatur es (25 and 17 degrees C). Hence, high temperature is primarily a facto r in providing conditions for the expression of genes determining the developmental rate, rather than a factor of selection for these genes. It is suggested that selected genes modify developmental rate depende nce on temperature.