Abstract:Artificially induced gynogenesis is a form of chromosome manipulation for sex control, accelerating both the elimination of recessive deleterious genes and the rapid establishment of inbred lines that could benefit the breeding progress in fish species. Artificially induced gynogenesis can be divided by mechanism into meiogynogenesis and mitogynogenesis. In this study, the fourth generation of a successive meiogynogenetic population (G4) in Japanese flounder (Paralichthys olivaceus) was established by induction of meiogynogenesis, in which the eggs of third-generation females (G3) were activated by ultraviolet-irradiated red sea bream (Pagrus major) sperm, followed by a cold-shock treatment at 0℃, starting 3 min after activation and lasting 45 min. We evaluated the genetic structure of the control, G2, G3, and G4 populations with 24 microsatellite markers and a high recombination rate that covered all linkage groups of the flounder. The efficiency of successive meiogynogenesis in terms of producing a highly inbred line was quantified by calculating the homozygosity and genetic similarity. The results showed that 96, 42, 32, and 32 alleles were detected in the control, G2, G3, and G4 populations, respectively; the average numbers of alleles were 4.00, 1.98, 1.33, and 1.33, respectively; and the average expected heterozygosities were 0.6416, 0.3472, 0.1694, and 0.1492, respectively. The average homozygosities among the 24 analyzed loci were 0.3503, 0.6528, 0.8306, and 0.8508, respectively. In the G4 population, 17 loci were homozygous, while 7 remained heterozygous. With respect to genetic similarity, the average similarity indexes between offsprings within populations were 0.5822, 0.9238, 0.9890, and 0.9988, respectively. Among G1, G2, and G3 populations, the homozygosity and genetic similarity index increased significantly (P<0.05) with generations. However, the differences in homozygosity and genetic similarity index between G3 and G4 were not significant. Our results indicate that artificially induced successive meiogynogenesis can effectively increase the homozygosity of individuals, as well as the genetic similarity of offspring within a population. Successive meiogynogenesis has a higher induction rate than mitogynogenesis, and therefore is a useful alternative method for establishing clonal lines in fish.
