Quantitative Trait Loci For Morphometric Body Measurements Of The Hybrids Of Silver Carp (Hypophthalmichthys Molitrix) And Bighead Carp (H. Nobilis)

Silver carp (Hypophthalmichthys molitrix) and bighead carp(Hypophthalmichthys nobilis) are two of the four most important pond-cultured fishspecies, which occupies important status in freshwater aquaculture in China. InRecent years, due to many factors such as increase of human population, theintensification of economical activity, inappropriate broodstock management,continuous artificial propagation over a long period of time has caused tremendousdecrease of genetic diversity and degeneration of disease resistance and growthperformance.With the rapid development of molecular biology, it is an effectiveapproach to cultivating the good strains using the combination of molecular breedingand traditional breeding for the sustainable development of the two fishes fishery andutilization of germplasm resources. In this study, genetic linkage map and QTLmapping of11morphometric body measurements of silver carp and bighead wereconstructed using microsatellite DNA markers, which provides strong support forpromoting the application of molecular genetics and breeding of silver carp andbighead carp.1．Construction of linkage map for silver carp and bighead carpIn this study， a segregating population including176fingerling individualsfrom cross between a wild bighead carp (♀) and a silver carp（♂）collected from themain channel of Yangtze River was obtained based on the double pseudo-testcrossmapping strategy.882pairs of microsatellites primers used for genotyping includedthose developed ourselves and other sources.297pairs of polymorphismmicrosatellites primers was used to construct the different genetic linkage maps of silve carp and bighead carp: the sex average linkage map, the female (bighead carp)linkage map, the male (silver carp) linkage map.The sex average linkage map consisted of247microsatellites (15microsatellitesdeveloped ourselves but unmapped on the linkage map of silver carp we constructedearlier) assigned to25linkage groups (including2triplets and2doublets) thatspanned a length of1010.4cM, covering81.0%of the estimated genome size. Themaximum and average spaces between233loci were24.8cM and4.4cMrespectively. The length of linkage groups ranged from1.2cM to67.5cM with anaverage of40.4cM. The number of microsatellite markers per group varied from2to19with an average of9.9.The female (bighead carp)linkage map consisted of180microsatellites assignedto30linkage groups (including4triplets and9doublets) that spanned a length of960.0cM, covering68.4%of the estimated genome size. The maximum and averagespaces between148loci were29.5cM and6.4cM respectively. The length of linkagegroups ranged from1.2cM to108.1cM with an average of32.0cM. The number ofmicrosatellite markers per group varied from2to16with an average of6.0.The male (silver carp)linkage map consisted of167microsatellites assigned to32linkage groups (including5triplets and9doublets) that spanned a length of803.1cM, covering66.4%of the estimated genome size. The maximum and averagespaces between133loci were30.6cM and5.9cM respectively. The length of linkagegroups ranged from2.3cM to99.9cM with an average of25.1cM. The number ofmicrosatellite markers per group varied from2to11with an average of5.2.2. Quantitative trait loci for morphometric body measurements of the hybrids ofsilver carp (Hypophthalmichthys molitrix) and bighead carp (H. nobilis)The location and effects of QTLs were estimated for body weight, standard length,body depth, body thickness, head length, head depth, length of ventral keel, length ofpectoral fin, length of pelvic fin, length of caudal fin, space between pectoral and pelvic fins traits using MapQTL5.0based on the sex average linkage map of silvercarp and bighead carp. Correlation coefficient of11phenotypic traits reached anextremely significant level. The Person coefficient was from0.950to0.996.11traitswere mapped at6QTLs on6linkage groups.The number of QTL of each trait rangedfrom1to6.The variance explained each locus ranged from9.1%to23.8%. It is alsovery interesting to note that many measurements were mapped on the same position;for example, a region bounded by Hym435and Hym145on linkage group19wasfound to be responsible for all the measurements analyzed in this study. Followinglinkage group19are linkage groups10and17, each contained QTL for8morphological characteristics. In addition, linkage groups4,5and9each were foundto hold QTL for2-4traits.