[The structure of the chromocenter in the oocytes, the initiation of homologous pairing and the regulation of the formation of crossing over in Drosophila]

Abstract

The structure of chromocenter and pairing of homologs in Drosophila oocytes with different X-chromosome inversions (sc7, sc9, BM1, y4, sc4sc8), and acrocentric compound C(1)DX were studied. Disturbances of chromosome pairing in compound C(1)DX, inversion of heterozygotes and some homozygotes (BM1, sc4sc8) were observed. Besides, disturbances of precentromeric heterochromatin regions pairing and nonassociation of X-bivalents with chromocenter were observed. It turned out that inversion loops were formed only in chromocenter formation peculiarities. It is supposed that disturbance of homologous pairing in inversion homozygotes is associated with transference of sites initiating the homologous pairing. These sites are in pretelomeric and adjacent heterochromatin regions. Interchromosomal effects of chromosome aberrations on crossingover and, probably, modification of its frequency by other factors are associated with the state of precentrometic heterochromatin homologous pairing in chromocenter. The formation of crossover exchanges is completed with a total pairing in these chromosome regions and subsequently with reorganization of the meiotic chromosome structure.