SEX-RATIO DEPRESSION AS A BROOD-PATTERN CRITERION OF RADIATION DAMAGE IN DROSOPHILA MELANOGASTER

The results of analyses of the brood variance in the relative frequency of females to males in the progeny of D. melanogaster males having structurally-normal chromosomes, not only established that there is a brood-curve of sex-ratio depression in the progeny of irradiated males, but also revealed that there was a curve of sex-ratio change in successive broods of offspring from unirradiated males even though the ratio of females to males in the total progeny was 1 : 1. The brood curve of sex-ratio change in both series of control males tended to be bimodal, with an increasing frequency of female offspring during the first five or six days, followed by a progressive decrease until about the 12th day, than subsequently an increase until about the 15-16th days, with perhaps again a decrease in the latest (17-24d) broods. The bimodality of the curve appeared to be the consequence of a complex relationship between brood-size, brood-rank and sex-ratio change. Following irradiation of the males with 3000r of X-rays, the incidence of female offspring decreased linearly for the first eight days, with a low of 44.32% in the 6-8d broods. This was followed by an abrupt return to a 1 : 1 sex-ratio in the 9th day and subsequent (10-24d) broods. The recovery of 50% female offspring in the 9th-day brood was interpreted as supporting evidence for the thesis that this brood was derived from cells that had been spermatogonia at the time of irradiation of the parental males. © 1968 Martinus Nijhoff.