QTL Analysis On The Growth Traits In Sea Cucumber

Thirteen single nucleotide polymorphisms (SNPs) were described incommercially important sea cucumber (Apostichopus japonicus). All loci had twoalleles and the minor allele frequency ranged from0.103to0.487. The observed andexpected heterozygosities ranged from0.154to0.769and from0.187to0.506,respectively. Only1of13loci deviated from equilibrium significantly due tohomozygote excess and no linkage disequilibrium was found. SNPs were developedin sea cucumber for the first time which may enrich the types of genetic markers usedin delineating population structure. Furthermore, the newly develpoed SNPs provide acomplement to currently available genetic markers.The linkage maps of A. japonicus were constructed with37primer combinationsof amplified fragment length polymorphism (AFLP) markers，which were genotypedin the parents and33progeny of the mapping family. Two genetic linkage maps wereconstructed using markers segregating in the female or the male parent, excluding thedistorted segregating ones. The female framework map was composed of106markersin17linkage groups, covering623cM with an average interval of7.0cM. The maleframework map contained104markers in20linkage groups, spanning568cM withan average marker density of6.9cM. The observed coverage was70.67%for thefemale map and66.47%for the male map.The map locations and effects of quantitative trait loci (QTL) were estimated for5growth-related characters in the sea cucumber based on the female and male geneticmaps. Twenty-one QTLs (LOD>2.0) were detected for five characters viacompositive interval mapping. The percentage of phenotypic variation explained by asingle QTL ranged from11.17%to32.68%. Seven QTLs were related to body lengthand located in different linkage groups of the male and female maps, suggesting thatthe trait may be controlled by multi-genes. Of the7body-length-related QTLs, one islinked with a body width-related QTL, and the genetic distance between them was4.0cM. Three QTLs located in LG13of the female map, LG3and LG4of the male map were detected for both body weight and body wall weight. Four QTLs related to themeat yield were located in4linkage groups (LG3, LG7, LG10of the female map, andLG10of the male map) explaining15.42-26.90%of the phenotypic variation.