Age-associated changes in viability genetic loads of Drosophila melanogaster

The effect of age upon genetic loads for egg-to-adult viability was analysed by comparisons of homozygous and heterozygous progeny of Drosophila melanogaster. Among 74 second chromosome groups of homozygotes, viability was significantly lowered when the chromosomes originated from 30–35 days old parents ($\text{x}\text{?}\text{=22·6 ± 1·2}\text{per cent}$) in comparison with the same chromosomes when they originated from the same parents at 1–5 days of age ($\text{x}\text{?}\text{=29·3 ± 1·4}\text{per cent}$). Among the heterozygous controls (N=37 chromosomal combinations) the viability was practically equal (30·5 ± 1·0 per cent and 30·2 ± 1·3 per cent) for the progeny of same parents when, respectively, 1–5 and 25–30 days of age. The viability of the second chromosomal homozygotes (N=48) whose parents were of quite different age (i.e. young mother $\text{x}\text{?}$ old father and vice versa) was insignificantly smaller than the viability of the heterozygous controls (28·7 ± 1·8 and 28·5 ± 1·8), showing an absence of maternal effect.