MAPPING AND GENETIC EFFECT ANALYSIS ON QUANTITATIVE TRAIT LOCI RELATED TO FEED CONVERSION RATIO OF COMMON CARP (CYPRINUS CARPIO L.)

The common carp (Cyprinus carpio L.), one of the most important species for aquaculture in China, is a widespread freshwater fish of eutrophic waters in lakes and large rivers. The wild populations are considered vulnerable to extinction, but the species has also been domesticated and introduced into environments worldwide, and is often considered as an invasive species. However, genetic degeneration, such as low growth rate, small body size, weak disease- resistance, etc., emerged in common carp with the rapid development of its farming scale. Quantitative traits (for example, the feed conversion ratio of common carp) refer to phenotypes that vary in degree and can be attributed to polygenic effects, i.e., product of two or more genes, and their environment. Quantitative trait loci (QTLs) are stretches of DNA containing or linked to the genes that underlie a quantitative trait. Mapping regions of the genome that contain genes involved in specifying a quantitative trait is done using molecular tags such as SSR, EST or more commonly SNPs. This is an early step in identifying and sequencing the actual genes underlying trait variation. Researches of genetic diversity, kin discrimination, strain identification, genetic linkage map construction, trait-related marker screening, genetic evaluation and QTL are the effective way to solve these problems of breeding in common carp. In this paper, a group of F2 hybrids German mirror carp including 68 individuals was used to construct a linkage map by using 560 markers (174 SSR markers, 41EST-SSR markers and 345 SNP markers). Quantitative traits loci (QTLs) associated with feed conversion ratio were identified by interval mapping and MQM mapping of the software MapQTL5.0. A linkage group wide permutation test (1000 replicates) determined the significance of the maximum LOD value over the various intervals analyzed for each linkage group. The results indicated that fifteen QTLs were identified for feed conversion ratio on nine linkage groups, which explained 17.70% and 52.20% of the total variation of feed conversion ratio, respectively. Two QTLs were associated with LG25 (HLJE314-SNP0919) and LG39 (HLJ1439-HLJ1438), which covered the lest 0.614 and most 24.922. There were two QTLs (HLJ1439-HLJ1438 and HLJ922-SNP0711), which explained over 50.00% of the total variation of the feed conversion ratio. They were major QTLs associated to the feed conversion of common carp. Three QTLs were negative additive effect with the average value of ?0.027, while the others positive additive effect with the average value of 0.06. The results also suggested that the feed conversion ratio traits should be determined by more than one loci which was conformed to the theory on quantitative genetics. This work investigated the correlation between markers and growth traits in common carp and obtained trait-related QTL and the results would be valuable for marker-assisted breeding in common carp.