Genetic Diversity Analysis Of Three Generations Of Selective Breeding Of Meretrix Meretrix

China is the largest artificial breeding and the largest number of marine mollusk in the world.Because of overfishing and disorder introduction, the marine mollusk resources in China havea greater negative impact.With the growing demand for marine mollusk, lack of improvedvarieties has become increasingly prominent.Heredity and breeding are playing an increasingimportant role in marine mollusk farming.High quality seed production program will be abasic trend in mollusk farming industry in future. In this paper, emphasize Status quo ofbreeding of marine mollusk,closely integrated genetic improvement and breed of new varietiesMeretrix meretrix,morphological markers and microsatellite markers were used to analysis thegenetic variation of breeding line of new varieties of Meretrix meretrix,which were kept inHard Clam Breeding Plant in Jiangsu.As a directive function for genetic improvement of breedof Meretrix meretrix.The cohort studies consisted of Two kinds of shell color clams（red and yellow）, Threegenerations, A total of seven groups, which were kept in Hard Clam Breeding Plant in Jiangsu.Parent of breeding of red shell color （PR）, Parent of breeding of yelow shell color （PY）,Children of the parent of red shell color was differentiation two kinds F1of red shellcolor（RF₁R）,F1of yellow shell coler（RF₁Y）, Children of the parent of yellow shell color wasall yellow shell color（YF1）,Parent of F2（RF₂, As the parent of F2,which choose the fast growthfrom RF₁R,）, F2of red shell color of RF₂（RF₂R）.First,used cluster analysis,principal component analysis and discriminant analysis of fivegroups of Meretrix meretrix（PR, PY, RF₁R, RF₁Y and YF1）. The result revealed, Significantdifferences between the individual of the various groups, there was rich genetic diversity ineach groups.the offspring of red shell color parents（RF₁R, RF₁Y） gathered together at first,then gathered together with the offspring of yellow（YF1）),while the the red shell colorparents（PR） and the yellow parents（PY） gather together, then those two sub-branches clusteredinto one group.In the principal component analysis,four principal component were constructed,the contributory ratio of the four principal components were23.132%,18.933%,16.555%and11.523%respectively, and the cumulative contributory ratio was70.143%. Second,genetic structure of five hard clam stocks were detected using nine pairs of SSRprimers and six ISSR primers. The shell color of one population is red and their offspring arered or yellow, while another population is yellow and their offspring are yellow also. Thesame as the first study（PR, PY, RF₁R, RF₁Y and YF1）.The PIC，observed and expectedheterozygosity of five populations detected from SSR ranged from0.643to0.7049,0.7455to0.7946and0.7175to0.752. The percentages of polymorphic loci detected from ISSR werefrom92.11%to97.37%. The highest Shannon Index from PR population was0.5033andlowest from RF₁Y was0.4126. Both the two markers showed high polymorphism. Comparedwith their parents’, the genetic structure of the three offspring populations didn’t changed. Theresults of cluster from the two kinds of markers were the same: the red shell color parents andtheir offspring gathered together at first, while the yellow parents and offspring gather together,then those two sub-branches clustered into one group. Overall, diversity detected in two kindsof molecular markers were at the same level, In other words, diversity did not changesignificantly after generation of breeding,the genetic diversity of the parents and theiroffspring were still very high, simultaneously, Increased reliability of the results of the twokinds of marker analysis.Final, ISSR-PCR were used to analye the genetic diversity of breeding populations the newvarieties of Meretrix meretrix of red color shell from2009. The research material consist ofPR, RF₁R, RF₂and RF₂R, Three generations,four groups. The result showed that the averageobserved allele number from1.8421to1.9737, the average effective allele number from1.4235to1.6079, the Nei’s genetic diversity from0.2581to0.357and the average Shannon’sgene diversity index from0.3987to0.5307. From largest to smallest, the genetic diversity ofthe four groups of Meretrix meretrix is RF₂、 PR、RF₂R、RF₁R respectively. The geneticdistance from0.0416to0.0569,the genetic identity from0.9447to0.9593; Dendrogram basedNei’s （1972） Genetic distance of microsatellite markers: Method=UPGMA，the red shellcolor parents（PR） and their offspring（RF₁R） gathered together at first, while the F2parents（RF₂） and F2（RF₂R）gather together, then those two sub-branches clustered into onegroup. After two generations breeding,the genetic structure of breeding population hasstabilized, with the increase of the breeding generations,The genetic distance between thevarious generations of breeding population with the wild population is gradually increasing,it’sreflects the role of artificial directional breeding, to prove the effectiveness of the breedingresults.To sum up the, next breeding of the RF₂R, we can keep a certain selection pressure, toimprove target traits, while, we should consider increasing the number of breeding parents, or re-introduction of wild populations with the target traits. Reduce the genetic recession becauseof inbred, Faster and more stable access the new varieties, gradual propagation and promotion,The research of breeding the new varieties to practical application in the production.