Institute Cytology and Genetics

Laboratory of Cell Division

Head B.F.Chadov, Dr.Biol.Sci.

Chromosome behavior (pairing, crossing-over, disjunction) in meiosis of D. Melanogaster. is under study. The main method is analysis of breeding data. From 1992, crossing-over has been investigated at the laboratory. A genetic model of crossing-over named the contact model was suggested. The model proposed that homolog pairing directly concerned with crossing-over is the sequential formation of local contacts between homologs (white knobs). Contacts become exchanges (black knobs) during crossingover determination (DCS -determination of crossingover sites common to the whole meiocyte). As the number of the contacts in the meiocyte reaches a definite threshold, the DCS (determination of crossing-over sites) occurs. Exchanges (black knobs) arise at the sites of contact that have the time to form at the onset of the DCS. The contacts arisen after the DCS serve only for pairing. The proposed model explains crossing-over variability in natural conditions, changes in crossing-over resulting from chromosome rearrangements. According to the model, chromosomal interference reflects the process of the extended establishment of local contacts between homologs. The model provides an explanation for the relationships between crossing-over and co-orientation of homologs in meiosis.