Genetic Studies On Gynogenetic Diploids In Mytilus Edulis And Patinopecten Yessoensis

Both Mytilus edulis and Patinopecten yessoensis are commercially importantmollusks species. In this study, we report the methods of inducing gynogenesis andgenetic analysis of the gynogenetic diploids in the two species.1. Genetic study on the gynogenetic diploids in Mytilus edulisGynogenetic diploids in M. edulis were induced by means of ultraviolet (UV)radiation and cytochalasin B (CB) treatment for the inhibition of the second polarbody release. The sperms irradiated by UV at an intensity of2561μW/(cm2·s) forvarious durations were fertilized with the normal eggs. With increasing irradiationtime, the cleavage rate, survival rate at early embryonic phase and developmental rateof D-larvae decreased, and none of D-larvae occurred at55s. Twenty-five minutesafter fertilization, the fertilized eggs were exposed to0.5μg/mL CB for20min.Microsatellite analysis demonstrated that100%of gynogenetic diploids weresuccessfully induced. Six informative microsatellite loci was examined in D-shapedlarvae of two induced meiogynogenetic diploid families of Mytilus edulis forcentromere mapping using half-tetrad analysis. The ratio of gynogenetic was provento be100%in all the two families, respectively. Inheritance analyses in the controlcrosses showed that all of the genotypic observed were in accordance with Mendelianexpectations at the5%level. One of the6microsatellite loci showed the existence ofnull alleles in the control crosses. The second division segregation frequency (y) ofthe microsatellite loci ranged from0.24to0.67with a mean of0.38.Microsatellite–centromere (M–C) distances ranged from12cM to34cM under theassumption of complete interference. 2. Genetic study on gynogenetic diploids in Patinopecten yessoensisWe induced gynogenetic diploids in P. yessoensis by means of ultraviolet (UV)radiation and utilized cytochalasin B (CB) treatment to inhibit the release of secondpolar body. The sperms irradiated by UV at an intensity of2561μW/(cm2·s) forvarious durations were fertilized with the normal eggs. With increasing irradiationtime, the cleavage rate, survival rate at early embryonic phase and developmental rateof D-larvae decreased, and none of D-larvae occurred at50s. Forty-five minutes afterfertilization, the fertilized eggs were exposed to0.5μg/mL CB for20min.Microsatellite analysis demonstrated that100%of gynogenetic diploids weresuccessfully induced. Inheritance of32informative microsatellite loci was examinedin70-h D-shaped larvae of three induced meiogynogenetic diploid families forcentromere mapping using half-tetrad analysis. The ratio of gynogenetic was provento be100%,100%and96%in the three families, respectively. Inheritance analyses inthe control crosses showed that51of the53genotypic ratios observed were inaccordance with Mendelian expectations at the5%level after sequential Bonferronicorrection. Six of the32microsatellite loci showed the existence of null alleles in thecontrol crosses. The second division segregation frequency (y) of the microsatelliteloci ranged from0.07to0.85with a mean of0.37, suggesting the existence ofpositive interference after a single chiasma formation in some chromosomes in thescallop. Microsatellite–centromere (M–C) distances ranged from4cM to42cMunder the assumption of complete interference. Information on the positions ofcentromeres in relation to the microsatellite loci will represent a contribution towardsassembly of genetic maps in the commercially important scallop species.