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.