Establishment of the diploid gynogenetic hybrid clonal line of red crucian carp x common carp.

This study investigated the gynogenetic cytobiological behavior of the third gynogenetic generation (G(3)), which was generated from the diploid eggs produced by the second gynogenetic generation (G(2)) of red crucian carp x common carp, and determined the chromosomal numbers of G(3), G(2)xscatter scale carp and G(2)xallotetraploid hybrids of red crucian carp x common carp. The results showed that the diploid eggs of G(2) with 100 chromosomes, activated by UV-irradiated sperm from scatter scale carp and without the treatment for doubling the chromosomes, could develop into G(3) with 100 chromosomes. Similar to the first and second gynogenetic generations (G(1) and G(2)), G(3) was also diploid (2n=100) and presented the hybrid traits. The triploids (3n=150) and tetraploids (4n=200) were produced by crossing G(2) with scatter scale carp, and crossing G(2) with allotetraploids, respectively. The extrusion of the second polar body in the eggs of G(2) ruled out the possibility that the retention of the second polar body led to the formation of the diploid eggs. In addition, we discussed the mechanism of the formation of the diploid eggs generated by G(2). The establishment of the diploid gynogenesis clonal line (G(1), G(2) and G(3)) provided the evidence that the diploid eggs were able to develop into a new diploid hybrid clonal line by gynogenesis. By producing the diploid eggs as a unique reproductive way, the diploid gynogenetic progeny of allotetraploid hybrids of red crucian carp x common carp had important significances in both biological evolution and production application.