Mapping and fine mapping of quantitative trait loci for the number of vertebrae in a White Duroc × Chinese Erhualian intercross resource population.

The number of vertebrae is associated with body size and meat production in pigs. To identify quantitative trait loci (QTL) for the number of vertebrae, phenotypic values were measured in 1029 individuals from a White Duroc × Chinese Erhualian intercross F(2) population. A whole genome scan was performed with 194 microsatellite markers in the F(2) population. Four genome-wide significant QTL and eight chromosome-wide significant QTL for the number of vertebrae were identified on pig chromosomes (SSC) 1, 2, 6, 7, 10 and 12. The most significant QTL was detected on SSC7 with a confidence interval of 1 cM, explaining 42.32% of the phenotypic variance in the thoracic vertebral number. The significant QTL on SSC1, 2 and 7 confirmed previous reports. A panel of 276 animals representing seven Western and Chinese breeds was genotyped with 34 microsatellite markers in the SSC7 QTL region. No obvious selective sweep effect was observed in the tested breeds, indicating that intensive selection for enlarged body size in Western commercial breeds did not wipe out the genetic variability in the QTL region. The Q alleles for increased vertebral number originated from both Chinese Erhualian and White Duroc founder animals. A haplotype block of approximately 900 kb was found to be shared by all Q-bearing chromosomes of F(1) sires except for one distinct Q chromosome. The critical region harbours the newly reported VRTN gene associated with vertebral number. Further investigations are required to confirm whether VRTN or two other positional candidate genes, PROX2 and FOS, cause the QTL effect.

A genome-wide scan reveals candidate susceptibility loci for pig hernias in an intercross between White Duroc and Erhualian.

Pig scrotal/inguinal and umbilical hernias are the most prevalent congenital disorders in pigs and often cause animal welfare problems and economic loss. To identify susceptibility loci for these traits, a genome-wide scan with 194 microsatellite markers covering the pig genome was performed in a White Duroc x Erhualian resource population with 23 scrotal/inguinal F(2) animals, 50 umbilical F(2) animals, and their unaffected siblings. A sex-average linkage map with a total length of 2,350.3 cM and an average marker interval of 12.84 cM was constructed. Both nonparametric genome-wide linkage (NPL) analysis and transmission disequilibrium test (TDT) were implemented to detect closely linked markers. The NPL analysis revealed 11 chromosomal regions on SSC1, 2, 3, 6, 7, 8, 10, and 11 for umbilical hernia and 5 regions on SSC2, 4, 8, 13, and 16 for scrotal/inguinal hernia, whereas the TDT test identified susceptibility loci for umbilical hernia on SSC1, 2, 4, 7, 10, 13, 14, and 15 and for scrotal/inguinal hernias on SSC2, 8, 10, and 18. The most promising loci were SWR1928 on SSC7 and SW830 on SSC10 for umbilical hernia, and SW933 on SSC8 for scrotal hernia, which were consistently detected by both NPL and TDT. Several previously reported chromosomal regions for scrotal/inguinal hernia were confirmed, and new evidence for linkage with this pig defect was found. Moreover, susceptibility loci for pig umbilical hernia were detected for the first time.