The effects of the promotor region of the 240bp repeats of the rRNA genes on x-y chromosome disjunction in Drosophila melanogaster males

Pairing between homologous chromosomes is essential for successful meiosis. In Drosophila melanogaster males, sex chromosome pairing during meiosis I is mediated by rDNA, located in heterochromatin. Several analyses of rDNA fragments showed that 240bp repeats in the intergenic spacer (IGS) have the ability to stimulate X-Y chromosome pairing and disjunction. In addition, point mutations within the promoter of the 240bp repeats failed to mediate X-Y chromosome pairing and disjunction. These previous studies imply that promoter activity of the 240bp repeats is involved in X-Y chromosome pairing in Drosophila males. In this study, I made a construct composed of 16 copies of the 72bp fragment within the 240bp repeat, which has promoter activity and obtained transformant lines with the construct. The construct was transferred to Df(1)X-1, an rDNA deficient X chromosome, by recombination. The effect of the transgene on the frequency of X-Y disjunction were analyzed both by cytological and genetic experiments. The transgene in Df(1)X-1 chromosome induced increased X-Y chromosome disjunction frequency. The result indicates that promoter activity of the 240bp repeats may be responsible for X-Y chromosome pairing in Drosophila males.