[The chromocenter structure in meiotic cells of Drosophila. Nonhomologous pairing].

The chromocenter is known as an integration of chromosome precentromeric heterochromatin regions. The squash technique was used for light microscopic analysis of chromocentral structures in Drosophila oocytes and trophocytes. The females displayed different structures of autosome 2. The precentromeric regions of autosome heterochromatin (chromocentral sites) were of different quantity (from 0 to 4). Cytological observations and frequency of non-incorporation of aberrant autosome 2 into the chromocenter have demonstrated that: 1) two chromocentral sites are required for an effective incorporation into chromocenter; 2) supernumerary sites are not involved in the chromocenter formation; 3) non-incorporation of chromosomes is caused by deletion of chromocentral sites; 4) chromocentral sites have some specificity because different bivalents with identical ones are competing for being incorporated into the chromocenter. A "multivalent" model of double circular structure of the chromocenter is proposed. The nature of connections between non-homologs is discussed in addition to the reason of bivalent location outside the chromocenter.