X-ray- and TEM-induced mitotic recombination in Drosophila melanogaster: unequal and sister-strand recombination.

Twin mosaic spots of dark-apricot and light-apricot ommatidia were found in the eyes of wa/wa females, of wa males, of females homozygous for In(1)sc4, wa and of attached-X females homozygous for wa. The flies were raised from larvae which had been treated with 1630 R of X-rays at the age of 48-52 hours. An additional group of wa/wa females and wa males came from larvae that had been fed with triethylene melamine (TEM) at the age of 22-24 hours. The twin spots apparently were the result of induced unequal mitotic recombination, i.e. from unequal sister-strand recombination in the males and from unequal sister-strand recombination as well as, possibly, unequal recombination between homologous strands in the females. That is, a duplication resulted in waDp wa/wa dark-apricot ommatidia and the corresponding deficiency in an adjacent area of wa/Df wa light-apricot ommatidia. In an additional experiment sister-strand mitotic recombination in the ring-X chromosome of ring-X/rod-X females heterozygous for w and wco is believed to be the cause for X-ray induced single mosaic spots that show the phenotype of the rod-X marker.