A cytogenetic study of radiation damage in entire genomes of drosophila

Abstract

Adult Drosophila melanogaster males, aged 1–2 days, were X-irradiated with 4000 R and mated for approximately 48 h to females containing genetic markers and/or crossover suppressors in all chromosomes. F1 females of the desired genotype were collected and appropriate genetic schemes followed to arrive at balanced stocks of entire treated genomes. Each chromosome of each genome was observed for visibles, lethals, sterility factors and extreme detrimentals. All chromosomes of each genome were examined cytologically for deficiencies, inversions, transpositions, etc., and to determine the breakpoints of translocations, previously detected genetically. Of the 310 genomes analyzed, 63.2% were found to contain genetic damage. It can be calculated that approximately 2265 genomes were actually irradiated, of which 10.7% transmtted genetic damage to succeeding generations. Inherited damage was tabulated in terms of damaged “sites”, a site being either a point mutation or a chromosome break. The number of sites in any particular genome varied from 1. to 6, there were on the average 1.12 sites per genome, and the average number of sites per chromosome was found to be related to mitotic length. Analyses were made of the interrelationships of the different types of damage by tabulating rearrangements according to cytological nature, viability, fertility and phenotypic expression, of recessive lethals according to cytological nature, and of visibles according to cytological nature, viability and fertility.