An Induced Maternal Effect on the Stability of the Ring-X-Chromosome of Drosophila Melanogaster

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Abstract
Male flies with the X-chromosome factors y w spl sn2 were irradiated and mated with Muller-5 females. When the F1 virgin females were mated with Xc2-ring males and the y w spl sn2 / Xc2-class of female offspring examined, the F1 flies mated within 2 days after emergence gave significantly fewer gynandromorphs than those aged 7 days or longer before mating. Similar trials using unirradiated chromosomes gave the same results. The percentage of gynandromorphs for unaged females ranged from 0 to 1.6 and for aged females from 2.0 to 8.0. In both the irradiated and non-irradiated series heterogeneity was statistically significant. Differences in percentage of gynandromorphs were observed among offspring from the first 24 hr. laying period of F1 females having diff. genotypes, but similar fluctuations were observed among repeated trials of the same cross. When mated F1 females were transferred daily to new cultures, the offspring from the 24-to 48-hr. laying period had a higher percentage of gynandromorphs than those from subsequent laying periods. Gynandromorphism was increased by aging the F1 females with fresh yeast and by using young males but was not affected by using XXY females. No gynandromorphs were found in crosses substituting for XC2 males those having a rod chromosome wild genotype or genetic markers. Elimination of the Xc2-chromosome accounted for nearly all the observed mosaicism, with 28% of this type being approx. bilateral gynandromorphs and almost 50% having one-fourth or more of the individual affected. Complete elimination of the Xc2-chromosome from all tissues was suggested by significant differences in sex ratios between unaged and aged females, and by indications that some M-5-males were of XO-constitution.

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