| Growth-related traits are of main interest for the genetic breeding program forswimming crab (Portunus trituberculatus). One of our goals of selective breedingprograms is to increase genetic response by affecting intensity and accuracy ofselection. Most traits of commercial importance are controlled by more than one locusthat are inherited quantitatively (Quantitative Trait Loci-QTL). Polymorphic QTL canonly be located using physically linked polymorphic marker loci. Thus, the first stepin identifying QTL is to develop a genetic map which have become essential tools inmany fields of genetic studies.To date, there are only a few studies on QTL affecting growth-related traits incrustaceans. One of the main reasons is the high cost required to overcome technicalbarriers involved in domestication, including selective breeding, maintaining highquality of domesticated brood stock, measuring animals and mapping the numerouschromosomes. P. trituberculatus crabs have substantially more chromosomes (2n=106) than most fish or shellfish; this means that more molecular markers are requiredto construct the same dense genetic linkage map used for QTL analysis.To fulfill the gap, a medium-density genetic linkage map of P. trituberculatusbased on microsatllite DNA markers and Amplifed Fragment Length Polymorphism(AFLP) primer combinations was constructed in110F2progeny of a full-sib family.Then, We locate25QTLs affecting10growth-related traits in P. Trituberculatus usingthe medium-density genetic linkage map. The work presented here should lay thefoundation for studies of marker-assisted selection (MAS) of the P. trituberculatus,eventually identifying individual genes responsible for growth-related traits.Firstly, total35microsatellite DNA markers were selected to analyze the geneticstructure of110individuals in an F2family which is obtained by directional matingtechniques for the selective program on fast growing P. Trituberculatus.(The F2family was created by F1family which was generated by wild populations from Laizhou Bay and Zhoushan Island.) The results showed that total87different alleleswere found, and the number of allele was2to4in each locus, with2.2effectivealleles on average. The value of mean observed heterozygosity, the value of meanexpected heterozygosity and the mean Polymorphism Information Content (PIC) was0.6465,0.5130and0.4491, respectively. The probability value of chi-square testshowed that most of the loci deviated from Hardy-Weinberg equilibrium significantly.The GLM procedure in SAS9.1was used to analyze the correlation between these35microsatellite markers and growth related traits of P. Trituberculatus. The growthrelated traits included full carapace width, body weight, carapacel width, carapacellength, body higth, second obital margin width, meropodit length of the claw,meropodit length of the first peraeopod. Results indicated that Pot08had a significantimpact on full carapace width, body weight, carapacel length, body higth, secondobital margin width; Pot42had a significant impact on body weight, carapacel length,meropodit length of the claw, meropodit length of the first peraeopod; Pot53had asignificant impact on carapacel width and meropodit length of the claw, and had avery significant impact on second obital margin width; Pot57and PTR30had asignificant impact on meropodit length of the first peraeopod and carapacel length,body weight, respectively; PTR8a had a significant impact on the first peraeopod andcarapacel length carapacel length, body higth, and had a very significant impact onbody weight, second obital margin width, full carapace width and carapacel width;PTR131had a significant impact on body weight, full carapace width and carapacelwidth. Finally, PTR8a can be used for marker assisted selection which aimed to bodyweight selection.A genetic linkage map of the P. Trituberculatus was constructed using the simplesequence repeat (SSR) markers and amplified fragment length polymorphism (AFLP)techniques. An F2family was created consisting of110individuals using the“two-way pseudo-testcross” mapping strategy. A total of1,294polymorphic markers,including55SSRs and1,239AFLPs, were used in the linkage mapping. Out of1,294markers,919(71%) were grouped on the two parental maps, leaving375(29%)unlinked. The female linkage map consisted of479marker loci (22SSRs and457AFLPs) which formed51linkage groups with an average marker spacing of7.8cM;they spanned a total length of3521.3cM, covering74%of the estimated genome size.The male map consisted of440marker loci (19SSRs and421AFLPs) which mapped to50linkage groups with an average marker spacing of8.7cM. They spanned a totallength of3517.6cM, covering75%of the estimated genome size. This map is the frstmedium density genetic linkage map in the family Portunidae and is a basicframework for further mapping quantitative trait loci (QTL) linked to importanteconomic traits of the swimming crab.In order to find the genes and genome area respond to growth-related traits. Weused a previously published genetic linkage map of P. trituberculatus, containing55simple sequence repeat (SSR) markers and172amplified fragment lengthpolymorphism (AFLP) techniques to map quantitative trait loci (QTL) forgrowth-related traits in a single full sib F2family. Ten growth-related traits weremeasured for QTL mapping. Composite interval mapping identified9QTL on thefemale map and16on the male map. Individual QTL with additive effectsexplained11%to38%of the phenotypic variance for various traits using the femaleparent’s map, and from1%to21%using the male parent’s map. Two QTLexplaining a large percentage of variation in body weight were detected onchromosome17on the female map, and on chromosome16on the male map, andcontributed38%and18%of the phenotypic variance, respectively. This is the frststudy to report the detection and positioning of major QTL affecting growth in atrue crab species (Brachyura). The mapping of growth-related QTL in this studyraises the possibility of improving the growth of P. trituberculatus throughmarker-assisted selection. |
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