Multiple vital functions of the daughterless (da) gene in Drosophila melanogaster and factors influencing its expression.

Multiple sub-vital effects, here designated as reductions in fitness S1-S5, for the second chromosome gene 'daughterless' (da) of Drosophila melanogaster were described as (S1) a recessive maternal lethality for daughters, (S2) a reduced fertility of da/da females, (S3) a recessive sub-vital zygotic effect, (S4) a recessive female-specific zygotic effect and (S5) a recessive maternal interaction effect on sons. (For S1-3 see also: Bell, 1954; Sandler, 1972; Cline, 1976). These five distinct effects were initially quantified from estimates of viability in single generation crossing experiments. Dynamic estimates of these fitness parameters were obtained by fitting the elimination rate of da from a series of large random mating cage populations to a recurrence equation by the method of minimum chi-square. The stability of these estimates discerns those effects which are truly pleiotropic versus those due to linked genes. The dynamic estimates supported only S1 and S4 effects. Evidence for S2 and S5 was indeterminate, but the S3 effect was rejected (P less than 0.01). The observed reduction in fitness, supposedly due to this recessive zygotic effect for da, was most likely the result of linked deleterious genes. These results indicate that pleiotropic vital effects observed in single generation test-cross matings may be caused by linked genes rather than the specific mutant per se. This problem is of particular importance when the mutant allele has been maintained with a balancer chromosome. Experiments on the rescue of daughters from da/da mothers with low temperatures during embryogenesis and with dechorionation of eggs were described in which the findings failed to confirm previously reported actions of the da gene. Modifying genes rather than environmental variables were cited as the probable cause for these conflicting results.