Analysis Of Genetic Background And Screening Of Genetic Markers For Specific Traits In Litopenaeus Vannamei Population

At present,the domestic shrimp Litopenaeus vannamei mainly comes from the foreign.There is no breeding company that can complete all the processes of genetic breeding in china.The main brand of domestic seed is from research institutions.Relatively small market competitiveness.Our country is the breeding of Litopenaeus vanname country,but due to improper farming,fry quality problems,financial problems,disasters and other factors,the breeding benefit loss still affects the healthy development of China’s shrimp industry system.In order to protect and develop germplasm resources,new varieties with good traits were obtained.In this paper,we analyzed the genetic background,identified the germplasm resources,and tested the growth of some SSR,screened some EST-SSR markers related to growth.And some molecular markers were tested for body weight.In the identification of the population in the family,through the comparison of the mtDNA control region sequence in different individuals,the maternal genetic relationships between 4 populations（VG2Z,VNZ,OSZ,NSZ）were obtained,and the variation and evolution among different maternal families were compared according to the genetic distance of the maximum likelihood method.The average length of the 211 sequences was 604 bp,and 232 parsimony information loci were detected.14 deletions.358 conserved loci,.281 mutations.Of the 232 point mutations,14 deletions / insertions,28 conversions,and 36 replacements were detected.A total of 14 haplotypes were detected,of which 27 haplotypes were detected in 14 parents.A total of 12 haplotypes were detected in 184 samples from offspring.Haplotype diversity index was 0.8950,nucleotide diversity index was 0.1100,average nucleotide difference was K65.1.The haplotype diversity index was 0.7980,the nucleotide diversity index was 0.1028,and the average nucleotide difference was K60.6.Genetic distance was calculated by the maximum likelihood method.The genetic distance was 0.156 within the parental（maternal）population,the genetic distance was 0.134 in the offspring population,and the genetic distance between the two generations was 0.144.Comparing the sequences of parents and their offspring,the Hd,PI,K and PL values of parents（mother）are greater than those of offspring.This indicated that the genetic diversity of F1 population decreased.There were 5 parents（females）in 27 parents（3 females）,and no haplotypes were detected in F1.1 new haplotypes Hap₈ were detected in the progeny group.Compared with Hap₇,2 conversions and 1 insertions occurred in the noncoding region of Hap₈,and the individuals with point mutations came from the self generation of the OS population.With the data of reproduction,8 female parents were confirmed by one to one.Evaluation of genetic diversity in 9 populations of 11 pairs of microsatellites.51 alleles were detected in 9 SSR populations of 11 generations.The number of alleles was 30⁵0,the number of effective alleles was Ne 22.09²8.39,and the observed heterozygosity was Ho 0.32⁰.60,and the expected heterozygosity was He 0.48⁰.63.Inbreeding coefficient in population was FIS-0.2⁰.37.The Shannon index index of hybrid population was 0.94,which was less than 1.13 of the inbred population,and the order from high to low was: selfing population > parent population > hybrid population.Compared with the inbred population,the diversity of hybrid population did not increase.The fixed index F of VNZ and G2 Z groups were-0.2 and-0.08,respectively.Other groups are positive.The present status of heterozygote deletion in G2 Z and VNZ heterozygotes and total population levels was demonstrated.The PIC range of the 9 populations at 11 SSR levels was 0.40⁰.59.The population is medium and highly polymorphic.The inbreeding coefficient Fit of the total population ranged from high to low: parent population > hybrid population > selfing population.Na,NSZ,G1 Z,G2Z,and OSZ were less than OSQ,NSQ,G1 Q,and G2 Q populations in the parental population,indicating that some rare alleles in the parental population were lost in the progeny.V101Z（Na）is greater than V101Q（Na）,which may have mutated or out of alleles from paternal sex.Ne and He were compared between inbred populations and their parents.The results showed that there was no significant difference between the inbred population and the corresponding parents.UPGMA phylogenetic tree was drawn by Nei’s genetic distance.The results showed that the genetic distance between 9 populations was 0.0685⁰.6065.The genetic distance between VNZ and OSZ is the shortest,and the priority is one.G2G1 Z and VG2 Z merge into one,then join with VG1 Z and NSZ,then merge with VNZ and OSZ,merge with G1 Z and G2 Z,and finally merge with V101 Z.The genetic distances between V101 Z and the other 8 populations were relatively remote.Genotype of EST-SSR primers with good polymorphism was associated with growth traits of Litopenaeus vannamei.Using the general linear model and the least square correlation analysis,we found that in the VG2 Z,4 microsatellites were significantly related to the growth traits by using the general linear model and the least square analysis of variance.Among them,V-16 was related to the significance of plumpness（P=0.10）,and LVE66 F was significantly related to body weight（P<0.1）.V-6 and LVE16 F were significantly related to body weight（0.10<P<0.05）.Other markers were unrelated to weight and plumpness.Duncan multiple comparisons showed that LVE16 F,LVE70F,and V-6 genotypes were not linearly related to body weight in VG2 Z,and the weight of BD genotype individuals in LVE66 F was significantly greater than that in AB/BB/BF individuals.But in other groups,LVE66 F was not significantly related to body weight and plumpness（P>0.05）.The correlation between 12 microsatellite markers and body weight and plumpness was examined using the intersubjective effect model,and LVE16 F and LVE70 F were significantly associated with body weight or plumpness in 4 populations（P<0.05）.The LVE16 F and LVE70 F Duncan s multiple mean value analysis results showed that the LVE16 F and LVE70 F genotypes in VG2 Z weight and no linear relationship exists in VNZ,the individual average weight of AB genotype LVE70 F was significantly greater than that of AA genotype.The body weight and plumpness of individuals with AA,BC,and BB were significantly greater than those of CC individuals,and the body weight and plumpness of individuals with the AA genotype were significantly greater than those of individuals with AB genotype LVE16 F.LVE70F and LVE16 F have a significant linear relationship with body weight and plumpness in VNZ.In G2 Z,the weight of LVE70 F,AB,BB individuals was significantly greater than BC,CC.The weight of AA,AB and BB individuals was significantly greater than that of CC,and the plumpness of individuals with CC genotype was significantly less than that of AA,AB and BB individuals.The weight of individuals with LVE16 F and AC genotypes was significantly greater than that of the BC genotype.In V101 Z,the weight of LVE70 F,AB,BB,AB individuals was significantly larger than that of BC individuals,and the plumpness of AA individuals was significantly greater than that of BC individuals.In LVE16 F,the body weight and plumpness of individuals with AC genotype were significantly greater than those of BC individuals.The allele C of LVE16 F and LVE70 F is recessive,and the weight of individuals with C is small.To sum up,this paper provides some theoretical basis for the germplasm selection of the artificial breeding population of Litopenaeus vannamei,and provides some theoretical basis for the selection of growth related molecular markers,and has certain guiding significance in production.