Study On Early Embryonic Development And RAPD Analysis Of The Diploid Gynogenetic Progeny Of Allotetraploid Hybrids

The diploid gynogenetic hybrids producing diploid eggs is a characteristic and an importance phenomenon of biology. The allotetraploids possesse 4 sets of chromosomes, and produced the diploid gametes. Without the treatment for doubling the chromosome number, the diploid eggs, produced by the allotetraploids, developed into the first-generation diploid gynogen (G₁) following activation by ultraviolet irradiating sperm. Interestingly, like the diploid F₂ hybrids, the G₁ also produced diploid eggs. Furthermore, the second-generation diploid gynogen (G₂) and the third-generation diploid gynogen (G₃) were produced with the same method of producing G₁. In the present paper, the early embryonic development of G₃ was observed, the genetic diversity and genetic purity in the G₂ and G₃ were analyzed by using random amplified polymorphic DNA (RAPD) assay.1 Observation on early embryonic development of gynogenetic progeny from alloteraploid hybridsFollowing activation by UV-irradiated sperm from scatter scale common carp and without the treatment for dubling the chromosome number, the eggs generated by G₂, developed into normal living G₃. The process of the early embryonic development of G₃ was similar to theprocess of the allotetraploid hybrids. The eggs of G2 were stick, the pigment of the eggs was high. The G2 produced three types of eggs, the one was haploid egg, its diameter was 1.35mm, its proportion was 2.47%, the other was diploid eggs, its diameter was 1.74mm, its proportion was 95.64%, the last was polyploid eggs, its diameter was 1,93mm, its proportion was 1.89%. At the water temperature of (19+ 1)°C, the eggs began the first cleavage at 70 min after fertilization and hatched out at 106.5 hours after fertilization. The passing gastrula and hatching rate of eggs was 50% and 26.11%. This study proved that the diploid eggs generated from the diploid gynogenetic hybrids were able to develop into the living progeny without the treatment for doubling the chromosome number. 2 RAPD analysis between G2 and G3The genetic diversity and genetic purity in the G2 and G3 were analyzed by using RAPD assay. Of 300 10-nucleotide-long random primers used in the preliminary analysis, 48 primers produced well-amplified and reproducible band patterns. They were selected and used in the further analysis in 8 of G2 and 8 of G3. The number of loci detected was 406 in G2 and 389 in G3. 6366 ( 3272 in G2 and 3094 in G3 ) distinguishable fragments were compiled for phylogenetic relationship analysis, the average fragments were 8.52 in G2 and 8.06 in G3. The number of polymorphic loci was 41 in G2 and 32 in G3. The percentage of polymorphic loci (10.10%) in G2 was considerately higher than that (8.23%) of in G3. The average genetic distances estimated by Lynchps index was 0.0224 in G2and 0.0201 in G3and 0.0358 between G2 and G3. Two primers, such as S129> S236, were observed to produce specific bands, and these bands could be used as molecular markers for discriminating the G2 from the G3. This study proved that through the gynogenesis, the G3 had higher genetic homozygosis than that of G2.