Studies On Molecular Genetics Of Japanese Scallop (Patinopecten Yessoensis)

1.Genetic variation in Chinese hatchery populations of the Japanese scallop(Patinopecten yessoensis)The Japanese scallop Patinopecten yessoensis was introduced to China about twodecades ago from Japan.In aquaculture,there are concerns as to whether geneticvariability would have been lost in farmed populations during their subsequenthatchery production.Using six microsatellite loci,three hatchery populations of P.yessoensis in China were compared with one another and with two wild Japanesepopulations.The hatchery populations were substantially less variable than wildpopulations.For the hatchery and wild populations,the average numbers of alleles perlocus were 5.7 and 7.9,and the average expected heterozygosities were 0.582 and0.671,respectively.This loss of variation is attributable to about 20 years of isolationand genetic drift.Fst values showed significant genetic differentiation among the fivepopulations.Genetic differences between the populations were also detected bypairwise comparison based on allelic distribution.The Neighbor-joining tree topologyconstructed on the basis of genetic distances among populations showed a cleardivision between the wild and hatchery populations.The information on the geneticvariation and differentiation in cultured and wild populations of P.yessoensis obtainedin this study is useful for setting up suitable guidelines for founding and maintainingof cultured stocks,and for future genetic improvement by selective breeding.2.A genetic map of the Japanese scallop Patinopecten yessoensis based AFLP andmicrosatellite markersWe constructed genetic linkage maps of the Japanese scallop Patinopecten yessoensis using AFLP and microsatellite markers.With 32 AFLP primercombinations,a total of 413 markers(209 from the female parent and 204 from themale parent) segregated in a 1:1 ratio,corresponding to DNA polymorphisms whichwere heterozygous in one parent and null in the other.Among the six microsatellitemarkers we used,there were four polymorphic loci.Two segregated in the femaleparent,and the other two segregated in both parents.In the maternal parent,161framework markers were mapped in 20 linkage groups,with a total coverage of2198.8 cM.In the paternal parent,166 framework markers established a map with 21linkage groups,spanning a genome length of 2137.6 cM.The AFLP markers on themaps were randomly distributed with an average spacing between markers of14.7-15.6 cM.The estimated coverage for the framework maps are 77.9% both forthe female and the male.These are the first linkage maps for P.yessoensis,whichconstitute a basis for further genome studies and provide a useful framework forconsensus map construction by adding orthologous anchor markers developed in P.yessoensis.3.Inheritance pattern of microsatellite loci and their use for kinship analysis inthe Japanese scallop Patinopecten yessoensisThe inheritance mode of seven microsatellite markers was investigated inPatinopecten yessoensis larvae from four controlled crosses,and the feasibility ofthese markers for kinship estimation was also examined.All the seven microsatelliteloci were compatible with Mendelian inheritance.Neither sex-linked barriers totransmission nor major barriers to fertilization between gametes from the parents wereevident.Two of the seven loci showed the presence of null alleles in two families,suggesting the need to conduct comprehensive species-specific inheritance studies formicrosatellite loci used in population genetic studies.However,even if the null alleleheterozygotes were considered as homozygotes in the calculation of genetic distance,offspring from four families were all unambiguously discriminated in theneighbor-joining dendrogram.This result indicates that the microsatellite markersused may be capable of discriminating between related and unrelated scallop larvae in the absence of pedigree information,and of investigating the effective number ofparents contributing to the hatchery population of the Japanese scallop.4.Inheritance of mitochondrial DNA in Japanese scallop Patinopecten yessoensisUntil now,mitochondrial inheritance in bivalves mainly focused on the familyMytilidae.We investigated the inheritance mode of a mitochondrial non-coding partin Japanese scallop Patinopecten yessoensis through ten families using DGGEanalysis.All of the progenies produced by these crosses had the mtDNA haplotype ofthe female parent,suggesting that inheritance of P.yessoensis mtDNA is maternal,and evidence for doubly uniparental inheritance(DUI) of mtDNA was found.5.Phylogenetic analysis of the family Pectinidae basing on completemitochondrial genomesMetazoan mitochondrial genomes usually consist of 37 genes.Such genes containuseful information for phylogenetic analyses and evolution modeling.We determinedthe complete sequence of the mitochondrial genomes of Chlamys farreri andMimachlamys nobilis,and described their gene contents and genome organizations toaccess their value for phylogenitic inference.The size of the mt-genome in C.farreriand M.nobillis are 21695 and 17693 bp,respectively.Both C.farreri and M.nobillismt-genome contained 12 typical protein coding genes,and lacked the Atpase subunit8 gene,as all published marine bivalves.In C.farreri a large non-coding region ispresent.Based on Japanese scallop and bay scallop mt-genomes sequence available inGenBank,we compared protein-coding gene arrangement of the four species ofscallop.We found the gene arrangement is similar among the four species.Neighbor-joining analyses on nucleotide of protein-coding genes of four species ofscallops suggest a close relationship of M.nobilis and P.yessoensis.