Fine Mapping And Verification Of QTL Affecting Growth-related Traits In The Linkage Group 1 Of Grass Carp(Ctenopharyngodon Idella)

Grass carp is one of the most important freshwater farmed fish in China.Traditional artificial breeding methods have a long breeding cycle,and marker-assisted selection(MAS)is an ideal choice to accelerate the breeding process and shorten the breeding cycle.In the research of genetic breeding of grass carp,traits about improving yield are often the focus of our attention,and studies on growth-related traits are also the most important part.Growth traits are important economic traits in aquaculture species,and are influenced by micro-effects of multiple genes and environmental factors.QTL mapping related to growth traits can be carried out to identify some candidate genes.In the early stage,preliminary QTL mapping for growth-related traits have been performed with a family of grass carp from the Yangtze River system,and a weight-related QTL(q BWH1)on the LG1 has been found.But it has not been further explored and utilized.Based on the previous experimental results,this study used STR typing and Interval Mapping(IM),combined with linkage analysis and association analysis,to further analyze and verify the QTL related to growth-traits in grass carp.The results are as follows:1.14 SSRs with polymorphism were developed successfully.In the F2 family of grass carp(n=275),QTL fine mapping in the LG1 were conducted with a total of 19 SSRs including the 14 developed SSRs and 5 existing markers.The results showed that19 SSRs were successfully linked to the LG1.The size of the LG1 was 82.5c M,and the average marker interval was 4.34 c M.With the availability of genotype information for each marker and individual,the map positions of all markers,and the data of the growth-related traits of the individuals,the q BWH1 was mapped between CID391?2and CID1512.And the size of the flanking marker interval was reduced from 32.4 c M to 7.5 c M.In addition,q BWH1?B was the newly detected QTL,located between CID973?1 and CID254?1.The interval of the flanking markers was 1.8 c M,and the genetic distance from the nearest marker CID254?1 was 0.8 c M.2.A selected population of grass carp from the Yangtze River system was constructed using 20 females and 24 males.Meanwhile,10 pairs of microsatellite primers were used to analyze the genetic diversity of the selected population.The results showed that the number of observed alleles(Na)of 10 loci in selected population was 13 to 23,The observed heterozygosity(Ho)is 0.804 to 0.919,the expected heterozygosity(He)is 0.826 to 0.911,and the polymorphic information content(PIC)is 0.808 to 0.903.The results reflected high genetic diversity of this selected population.Based on the genetic information of the candidate parents(n = 44)of the selected population,parentage test was used to the 480 offspring.The results showed that 98.3%(472/480)of the offspring could be assigned to candidate parents effectively.Based on the results of parentage test,heritability analysis of body weight and body length was performed on the selected population.The results showed that the heritability of body weight was 0.33 ± 0.19,and the heritability of body length was0.41 ± 0.22,which all showed moderate levels of heritability.3.To verify the results of QTL fine mapping in the LG1,by means of one way analysis and multiple comparisons of the genotypes and the growth-related traits,4flanking markers of the two QTL(CID391?2,CID1512,CID973?1,and CID254?1)were used to analyze the 480 individuals in the selected population of the grass carp.The results showed that these 4 markers were highly polymorphic in the population(PIC> 0.50).By means of oneway analysis and multiple comparisons of the genotypes and the growth traits(weight and body length)in the selected populations of grass carp.CID391?2 showed no significant difference between genotypes and the two growthtraits in female individuals(P> 0.05),while there was significant difference between genotypes and the two growth-related traits in male individuals(P <0.05);CID1512,CID973?1 and CID254?1 showed significant differences between each genotype and the two growth-related traits in female or male individuals(P <0.05).Meanwhile,the favorable genotypes of each locus were preliminarily determined.