title: Partial losses of sex chromosomes induced by X-rays in spermatozoa of Drosophila melanogaster.
abstract: The frequency of induced partial and complete losses of sex chromosomes from spermatozoa of Drosophila melanogaster was determined by mating irradiated males to females heterozygous for an attached-X Y chromosome and for a bb-deficient chromosome. The relative involvement of the X- and Y-chromosomes in partial losses was determined by (a) irradiating males with an X-chromosome centromere marked by a y+ translocated to the short right arm, and a Y-chromosome marked by w+, and (b) comparing the frequencies of fragments recovered from irradiated males with a normal, marked Y-chromosome and from irradiated males and a deleted bb Y-chromsome. 50-80% of the induced losses of sex-chromosomes in rod-X/Y males were partial losses, whereas only 25% of those induced in ring-X/Y males were partial losses. More than 70% of the recovered fragments were of Y-chromosome origin. Fragments recovered from attached-X-Y sons of irradiated males wer checked for the presence of the most proximal euchromatic X-chromosome genes. Most fragments of the rod-X were broken more proximally than bb. In the ring-X there was an excess of fragments broken in the proximal euchromatin. It was concluded that many fragments of the Y-chromosome was due to breaks induced by one-hit events, in both arms of the chromosome that were folded upon themselves. A similar mechanism had been postulated earlier for fragments of the ring-X chromosome.
mesh_terms: D000818:Animals; D002869:Chromosome Aberrations; D002872:Chromosome Deletion; D004331:Drosophila melanogaster / Q000528:radiation effects; D005260:Female; D008297:Male; D011831:Radiation Genetics; D012730:Sex Chromosomes / Q000528:radiation effects*; D013094:Spermatozoa / Q000528:radiation effects*; D014965:X-Rays