SYNTHESIS OF FREE X-DUPLICATIONS CARRYING A SPECIFIC REGION OF THE CENTROMERIC HETEROCHROMATIN IN DROSOPHILA-MELANOGASTER

Free X duplication chromosomes of Drosophila melanogaster were synthes ized by X-ray irradiating the In(1)sc(L8L)sc8R chromosome which has a deletion in the distatl half of hA and the proximal half of hB of the centromeric heterochromatin. Fifty-nine duplications have been isolate d and cytogenetically analyzed. They all carry wild-type allele of the yellow gene, y+, which should come from the distal tip of In(1)sc(L8L )sc8R. They appear to be telocentric and predominantly heterochromatic . Majority of the duplications, especially in the classes MEDIUM and L ARGE, can pair with XYL.YS in the male meiosis, indicating that they c arry male meiotic pairing site(s) that is known to be located exclusiv ely in the X heterochromatin. Complementation test in the males, Df(1) svr, v/Dp, y+, demonstrates that most of the duplications in the class es MEDIUM and LARGE carry euchromatin enough to cover the deletion. Th e portion of the euchromatin should be of the very proximal region clo se to the irradiated X chromosome centromere.