[Sex chromosome behavior in meiosis in the gray hamster (Cricetulus migratorius Pallas, 1770)].

The sequence of X and Y chromosomes pairing at meiotic prophase in the Armenian hamster Cricetulus migratorius Pall., 1770 gas been studied. The results of differential staining (C-, Ag-NOR) of mitotic chromosomes are presented. The rare case of interstitial synapsis of the sex chromosomes has been described. Earlier it was established only for Peromyscus sitkensis (Hale, Greenbaum, 1986). Pairing of the X and Y chromosomes is initiated at an interstitial position of the euchromatic region with subsequent synapsis towards the telomeres of the short arms. The latter conjugate completely and in this state do not differ outwardly from autosomal bivalents. The long arms remain asynaptic (heteropycnotic) constantly but at the meiosis undergo different morphological changes (thickness, bulging, clear showing filament structures, etc.) The data obtained agree with the hypothesis of Matthey (1961) claiming that the paired parts of X and Y chromosomes of the species with large Y chromosome and visible chiasma have autosomal origin. Therefore, X and Y chromosomes of Cricetulus migratorius could be originated via autosome-gonosome translocation.