ИСТИНА

Sterlet sturgeon Acipenser ruthenus and kaluga A. dauricus differ in their ploidy levels (Vasil’ev 1985, Vasil’ev et al. 2011). However, their hybrid males demonstrate enough high fertility (females are sterile). Thus, it was possible to obtain backcross hybrids A. ruthenus х (A. ruthenus х A. dauricus) (type ”a”) and A. dauricus x (A. ruthenus х A. dauricus) (type “b”). A number of assumptions were presented to explain hybrid fertility. One of them presumes that hybrid males produce sperm with haploid maternal genome (60 chromosomes), whereas paternal genome selectively eliminated (hybridogenesis). In this case hybrids of type “a” will have about 120 chromosomes and hybrids of type “b” – about 195 chromosomes. The karyological analysis revealed that ”a”-hybrids have 140-158 chromosomes (modal value 144-153), “b”-hybrids - 190-230 (modal value 209-220). Given the error of counting the chromosome number resulting from numerous microchromosomes, the fluctuation range of chromosome numbers can be considered not very large. As a result, two assumptions are possible. 1) Hybridogenesis takes place, but a small number of paternal (A. dauricus) microchromosomes is not eliminated and enter in spermatozoa. 2) Hybrid spermatozoa have different chromosome numbers, but only some of them (with 80-90 chromosomes) can result in viable backcross hybrids.