| Common carp (Cyprinus carpio L.) is one of the major aquaculture species in theworld, the global annual production of C. carpio is about3.7million tons. China is thelargest common carp farming and consuming country in theworld, with annualproduction of2.7million tons, which accounted for72.97%of world production.Meanwhile, the breeds of common carp are more than any other fish species, with a lotof variation in body shape, body color, scales and other phenotypic traits, which providea wealth of experimental materials to conduct genetic study and breeding for commoncarp.Common carp is also one of earlier fish species in which molecular breeding wasconducted. In the condition that molecular breeding technology based on the geneticbackground more and more matured in common carp, significant progress have alsomade in the screening trait associated markers and QTL mapping studies. Up tothousands of QTLs have been identified in common carp, including body weight,standard length, body height, body thickness, and other phenotypic traits; lactatedehydrogenase, superoxide dismutase, alkaline phosphatase, acid phosphatase, andother biochemical traits; muscle fiber density, fatty acids, and other meat qualitytraits.Assessment of breeding potential of these QTLs, identification of QTLs sharedbetween different families and varieties and exploring strategies for guiding molecularbreeding are premise to apply these QTLs in breeding practices.In this study, a full-sib family of mirror carp was referred as start point, dozens ofQTLs that control12growth traits were identified. These QTLs was validated in fivefamilies and QTLs shared between different families were identified. Furthermore,QTLs of mirror carp were applied in Jian carp and QTLs shared between these twomajor farming breeds of common carp were identified. Though analysing allelesdistribution of a large mount of QTLs in breeding populations, strategies were proposedto effectively enrich prefer genotypes in common carp. Finally, the FISH technique employed to located part of QTL intervals and linkage group on chromosomes. Themain results were listed as follows:(1)In a full-sib family of mirror carp (RR) comprising of68progenies, thecorrelation between164microsatellite markers from BAC end sequence (BES) and12growth traits were analyzed. Totally,401alleles consisting of456kinds of genotypeswere detected in these164microsatellite markers. By regression analysis under GLMmodel (Permutation10000times), There were40microsatellite markers correlated withat least one trait with significantly (P<0.05), among which eight markers (CA905,CA1175, CA1340, CA1526, CA1737, CA2117, CA2225and CA2334) were correlatedwith four or more traits significantly (P<0.05). The preferred genotypes of each markerwere detected by using Duncan’s multiple comparisons method implied in SPSS19.0.(2) These164BES originated microsatellite markers were added into the existinggenetic map of common carp, the new genetic map of common carp containing535marks (249microsatellite markers and286SNP markers), which distributed in50linkage groups. The total length of map was2244.655cM, the average interval betweenmarkers was4.628cM. QTL analysis of12growth traits detected65QTL intervals,these QTLs distributed in18linkage groups, phenotypic variation of each QTL intervalsvaried from9.9%to60.7%. Four QTL intervals were detected in body weight (qBW1-2),body length (qSL8), dody height (qBH1-2) and caudal peduncle height (qTH1-2), whichwere significant at genomic level. Further assessment of45microsatellite markerslocated in QTL intervals suggested that17microsatellites were significantly correlatedto at least one of the four traits, showing the close linkage with the QTL. The preferredgenotypes of these markers were also determined.(3)17QTL-linked markers of major growth traits were validated in five families(AA, BB, CC, DD, and EE) of common carp, and QTLs shared between families werealso identified. And then, enrichment and aggregation effects of preferred genotypes ofmultiple QTL markers were evaluated. The results suggested that17QTL markerssignificantly correlated with trait in at least one verified family. Out of these markers,HLJ365significantly correlated with certain traits in four families, and five markers(CA2117, HLJ401, HLJ668, HLJ404and HLJ322) significantly correlated with certaintraits in three families. The preferred genotypes of five QTL markers(CA2117, HLJ1113,HLJ057, HLJ404, and HLJE253) were consistent among six families, which these markers have good genetic stability. Further study found that62.94%of ten maximumbody weight individuals(Max group) contained the preferred genotypes of17QTLmarkers, while21.76%of ten minimum individuals (Min group) contained the preferredgenotypes. The result showed significantly different for enrichment of the preferredgenotypes in Max group and Min group. In addition, Max group contained the preferredgenotypes in7~14QTL markers, as well as Min group contained the preferredgenotypes in0~8QTL markers. These results suggested us we can increase the value ofthe target phenotypic traits by enriching and aggregating preferred genotypes of severalQTLs.(4) QTL intervals affecting body weight, standard length, body height, and bodythickness were detected in DD full-sib family of mirror carp. A total of54QTL markersand83preferred genotypes were identified by assessing the contribution of differentgenotypes on traits from89overlap and flank markers of QTL intervals.In addition, amapping population of Jian carp was analysed using54QTL markers from DD and17QTL markers from RR. Out of71QTL-linked markers,28markers were sharedbetween mirror carp and Jian carp, and23shared markers significantly correlated withthe same trait between the two breeds of common carp. Thirty-seven preferredgenotypes were identified from Jian carp, which can be used in breeding of Jian carp.QTL shared between species can be extended excavations of QTL usage, reducing theeffort and cost of QTL mapping innew varieties of common carp.(5) The genetic structures of three successive generations of breeding populationswere analysed using total45QTL markers and63non-QTL markers. The meanobserved heterozygous (Ho) by QTL markerswas lower5%than that of non-QTLmarkers in F0population. The number of effective alleles(Ne) by QTL markers waslower0.42than that of non-QTL markers in F1population, and the expectedheterozygous (He) and polymorphic information content (PIC) were lower5%. The fivegenetic parameters by QTL markers were lower than that of non-QTL markers in F2population. These results indicated that QTL-linked markers showed lower diversitythan non-QTL linked markers in artificial selection population. According to genotypefrequency and difficulty of breeding in single family and in the breeding population, thestrategies were proposed to effective enrich preferred genotypes in common carp, whichcan provide reference for QTL in molecular breeding applications. (6) the BAC clones containing target markers were taked as probes,18S rDNA andanother16markers located on13linkage groups (8linkage groups harboring QTLintervals) were successful located on the chromosomes by using FISH technique.18SrDNA were located on the short arms of a pair of sub-metacentric chromosomes; only apositive signal observed nine of16markers; seven other markers detected two positivesignals, combined with chromosome morphology judgment, CA2218-K02,CA2117-B08, CA1850-P24, CA1623-K17, CA1842-H15and CA2278-L18wererespectively positioned on one pair of homologous chromosomes are, while the twopositive signals CA1757-A12are located in the end of a telocentric chromosome (T)and near the centromere position of another one. Though the shape of the two Tchromosomes are similar with each other, if it is a pair of homologous chromosomescan’t be accurately judged. There were two markers observed LG11, LG12and LG15,the relative position of FISH resultswere similar to these of markers on the genetic map. |
PDF Full Text Request