The formation of a diploid gynogenetic hybrid clonal line of red crucian carp x common carp, and its application
Diploid eggs produced by allotetraploid hybrids were able to develop into a first gynogenetic generation (G1, 2n = 100), without treatment for doubling the chromosome number. Interestingly, G1 hybrids were all female and were able to produce a great number of diploid eggs, which developed into the second gynogenetic generation (G2, 2n = 100) in the same way as G1. Until now, the third (G3) and fourth (G4) gynogenetic generation (2n = 100) were formed in the same way as G1 and G2. Thus, a diploid gynogenetic hybrid clonal line (G1, G2, G3 and G4) of red crucian carp x common carp was established. It was concluded that the formation of diploid eggs produced by diploid hybrids was probably due to the pre-meiotic endoreduplication in the early oogonia. Diploid gynogenetic hybrids grew faster and had higher anti-disease ability than allotetraploid hybrids. The improved tetraploid hybrids (G1 x 4n) were formed by crossing diploid eggs of G1 with the diploid sperm of the allotetraploid hybrids. After mating, 98% G1 x 4n hybrids produced tetraploid hybrid offspring with 200 chromosomes. But 2% of G1 x 4n hybrids produced three types of diploid offspring with 100 chromosomes: red crucian carp with a single tail, goldfish with a biforked tail and common carp with a single tail, suggesting that gynogenesis made G1 x 4n hybrids produce diversified progeny. Furthermore, red crucian carp males and females interbred to produce three other kinds of fish: coloured crucian carp, black crucian carp and red crucian carp. This study indicated that the diploid gynogenetic hybrid clonal line of red crucian carp x common carp had important significances both in terms of evolution and its genetic breeding application.