Polyploidy in germ cell of brown bear Ursus arctos (Ursidae, Mammalia): A case report.

In this work, we present the first detailed study of the normal meiotic karyotype of the brown bear based on the analysis of synaptonemal complexes. Microphotographs of the key stages of meiotic prophase I were obtained. The level of meiotic recombination, features of XY sex bivalent assembly during meiotic prophase I were analyzed. A refined SC karyotype ideogram was constructed, consisting of 37 pachytene bivalents: 36 autosomal bivalents and and XY sex bivalent. We report a rare finding in mammalian germinal cells - a polyploid spermatocyte after genome duplication in the brown bear Ursus arctos. Meiotic tetravalents typical of autotetraploidy, the synaptic configurations consisting of homologous chromosomes and their corresponding duplicated copies, were visualized in this unique nucleus.