Reduction in Productivity and Recessive Lethal Mutation Following X-Irradiation CF Female Drosophila melanogaster

Sex-linked recessive lethals were recovered from successive batches of eggs laid by female Drosophila melanogaster irradiated with 4,000 r of X-rays. While the initial frequency of lethals (10 per cent.) is similar to that of males treated in an identical manner, there is an immediate linear decline in lethal frequency which reaches a value only 60 per cent. the initial frequency in eggs laid 7-12 days after irradiation. The decline in frequency is taken to represent the elimination in immature germ cells of induced lethal effects belonging to the class of chromosome aberrations. The fecundity and/or fertility of irradiated females is greatly reduced for the first four days after treatment. A rise in female productivity occurs between days 4 and 5. After a week has passed the productivity of treated females is almost normal, although the eggs produced by the females contain 60 per cent. as many sex-linked lethals as the eggs produced immediately after irradiation. The rise in productivity of females from four to five days after treatment is explained by assuming that the eggs laid at this time were 16-cell cysts at the time of irradiation and were resistant to irradiation in much the same fashion as is polyploid tissue.