A genome scan revealed significant associations of growth traits with a major QTL and GHR2 in tilapia.

Growth is an important trait in animal breeding. However, the genetic effects underpinning fish growth variability are still poorly understood. QTL mapping and analysis of candidate genes are effective methods to address this issue. We conducted a genome-wide QTL analysis for growth in tilapia. A total of 10, 7 and 8 significant QTLs were identified for body weight, total length and standard length at 140 dph, respectively. The majority of these QTLs were sex-specific. One major QTL for growth traits was identified in the sex-determining locus in LG1, explaining 71.7%, 67.2% and 64.9% of the phenotypic variation (PV) of body weight, total length and standard length, respectively. In addition, a candidate gene GHR2 in a QTL was significantly associated with body weight, explaining 13.1% of PV. Real-time qPCR revealed that different genotypes at the GHR2 locus influenced the IGF-1 expression level. The markers located in the major QTL for growth traits could be used in marker-assisted selection of tilapia. The associations between GHR2 variants and growth traits suggest that the GHR2 gene should be an important gene that explains the difference in growth among tilapia species.

A microsatellite-based linkage map of salt tolerant tilapia (Oreochromis mossambicus x Oreochromis spp.) and mapping of sex-determining loci.

BACKGROUND: Tilapia is the common name for a group of cichlid fishes and is one of the most important aquacultured freshwater food fish. Mozambique tilapia and its hybrids, including red tilapia are main representatives of salt tolerant tilapias. A linkage map is an essential framework for mapping QTL for important traits, positional cloning of genes and understanding of genome evolution. RESULTS: We constructed a consensus linkage map of Mozambique tilapia and red tilapia using 95 individuals from two F1 families and 401 microsatellites including 282 EST-derived markers. In addition, we conducted comparative mapping and searched for sex-determining loci on the whole genome. These 401 microsatellites were assigned to 22 linkage groups. The map spanned 1067.6 cM with an average inter-marker distance of 3.3 cM. Comparative mapping between tilapia and stickleback, medaka, pufferfish and zebrafish revealed clear homologous relationships between chromosomes from different species. We found evidence for the fusion of two sets of two independent chromosomes forming two new chromosome pairs, leading to a reduction of 24 chromosome pairs in their ancestor to 22 pairs in tilapias. The XY sex determination locus in Mozambique tilapia was mapped on LG1, and verified in five families containing 549 individuals. The major XY sex determination locus in red tilapia was located on LG22, and verified in two families containing 275 individuals. CONCLUSIONS: A first-generation linkage map of salt tolerant tilapia was constructed using 401 microsatellites. Two separate fusions of two sets of two independent chromosomes may lead to a reduction of 24 chromosome pairs in their ancestor to 22 pairs in tilapias. The XY sex-determining loci from Mozambique tilapia and red tilapia were mapped on LG1 and LG22, respectively. This map provides a useful resource for QTL mapping for important traits and comparative genome studies. The DNA markers linked to the sex-determining loci could be used in the selection of YY males for breeding all-male populations of salt tolerant tilapia, as well as in studies on mechanisms of sex determination in fish.

[Sequencing analysis on partial translated region of uncoupling protein-3 gene and single nucleotide polymorphism associations with the porcine carcass and meat quality traits].

Porcine uncoupling protein-3 gene was used to study its effect on carcass and meat quality traits. The UCP3 partial translated regions in skeletal muscle from four pig breeds were sequenced and the comparison of the fragment sequences among four pig breeds showed that there were three coding-region single nucleotide polymorphisms (cSNP), of which the mutation at 842 bp of the open reading frame can result in the amino acid chang between methionine and threonine, so we selected the mutation as polymorphic site. The detection of polymorphic fragment by the technique of single strand conformation polymorphism (SSCP) and chi2 analysis among three pig breeds indicated that the distribution of three genotypes(AA, AB and BB) was significantly different between Meishan and Large White or Meishan and Landrace( P < 0.01). In addition, association analysis of UCP3 polymorphism with carcass and meat quality traits was conducted in the F2 generation from the Large White x Meishan resource family, the results with GLM analysis showed that UCP3 polymorphism has significant effect on several carcass and meat quality traits and also additive effect on some carcass and meat quality traits predominated in the resource family. It implied that UCP3 gene could be a candidate gene locus or a linked marker to a major gene, which affects the porcine carcass traits and meat quality traits significantly.