| Final dissection of the molecular mechanisms underlying economically important traits will be applied in animal breeding programmes to ameliorate the genetic resistance of disease, and to improve production efficiency and product quality. Information acquired from quantitative trait loci (QTLs) mapping and developmental genetic research of quantitative traits could help to determine the optimized stages for early selection. Combined the fruits of genome research with the sophiticated statistical and computational tools that have much greater power than ever, QTLs have been mapped and cloned in numerous organisms.An F2 chicken population of 437 individuals, obtained by reciprocally crossing White Plymouth Rock with Silkies, was used for detecting and mapping QTLs. Fluorescent-labeled microsatellite primers of 264 pairs in total have been employed to perform genome scanning. Those microsatellite markers, distributed on 33 linkage groups, were largely polymorphic and could be used to scan the chicken genome to get information of the interested traits.QTL regression interval mapping was performed based on the CAU genetic linkage map constructed with 228 pairs of microsatellites, which covered 4774.1 cM with the average marker density 20.9cM. At the same time, genetic mapping of some functional genes (Lmbrl, MC4R and IGF1) with their SSCP (single- stranded conformational polymorphism) genotypes was analyzed along with microsatellite markers in CAU genetic map. IGF1 was mapped on GGA1, linked with UMA1.145 (LOD value 5.26). Lmbrl and MC4R were both located on GGA2, in marker interval MCW0082-ADL0270 and MCW0034-LEI0195, and they were linked with ADL0270 and LEI0195 (LOD values 20.77,10.39), respectively.QTLs affecting the interested traits have been identified, and candidate gene was screened in the related regions. Crest type was related with a corresponding locus on GGA4, and possibly the complex (V-shape and Cup-shape) locus. There were 4 QTLs on Chromosomes 2,3,5 and 13 affecting polydactyly, and possibly related with candidate genes Lmbrl, WNT3A, WNTJ1 and WNT8A, respectively.Development of chicken visceral organs was regulated by different signal pathways, on which many genes interacted with each other and constituted a metabolic network. Heart weight was related with two QTLs on chicken chromosomes 4 and 5, and further investigation indicated those loci might be linked with candidate genes FGF2, HTR1D or TGFB3, respectively. Breast width, shank girth and length of small intestinal were affected by a pleiotropic QTL on GGA1 positioned at 281cM, and LDHB located ajt this region, which could be considered as the candidate gene.Abdominal fat weight was affected by four loci on chromosomes 1,4,5 and 10 with LOD scores 2.84, 2.24,2.27 and 2.24, and might relate with four candidate genes UCP2, CAPN1, FGF2 and IGF1R, respectively. Intramuscular fat content was affected by QTLs on chromosomes 5-8, 15, 17 and 28, respectively, and on GGA7, NAB1 and GDF8 (Myostatin) might be the best candidates for further study.Conditional analyses on growth traits showed that body weights before or after 2-3 week-age, were regulated by two different sets of gene systems with various molecular bases and physiological effects. Animal growth was controlled mainly by growth hormone (GH) axis. Major effect of GH was regulated by 1GF-1 after 2-3 week. However, IGF-2 also played an important role before 2-3 week.
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