Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 1, 2002
Publication Date: July 1, 2003
Citation: CAMPBELL, E.M.C., NONNEMAN, D.J., ROHRER, G.A. FINE MAPPING A QTL AFFECTING OVULATION RATE IN SWINE ON CHROMOSOME 8. JOURNAL OF ANIMAL SCIENCE. 2003. v.81. p. 1706-1714. Interpretive Summary: A QTL has been detected affecting ovulation rate on the terminal end of chromosome 8p. Additional genetic markers were developed for this region using a directed comparative mapping approach by selecting genes that mapped to HSA 4p16-15. This approach permitted a high-resolution comparative map for SSC 8p2.3 and provided a sufficient number of markers to determine if this QTL is segregating in commercial swine populations. Nine genes were localized to the first 8 cM of the linkage group but only three are within the confidence interval of the QTL in this study. The next phase of this research is to utilize the genetic markers in commercial swine populations where ovulation rates have been measured to determine if this QTL is segregating in commercial pigs. In addition, positional candidate genes can now be selected from the human genome sequence located within the first 10 Mb of HSA 4 and evaluated in the founding animals of the MARC swine resource population.
Technical Abstract: Ovulation rate is an integral component of litter size in swine, but is difficult to directly select upon in commercial swine production. Since a QTL has been detected for ovulation rate at the terminal end of chromosome 8p, genetic markers for this QTL would enable direct selection on ovulation rate in both males and females. Eleven genes from human chromosome 4p16-p15 as well as one physiological candidate gene were genetically mapped in the pig. Large insert swine genomic libraries were screened, clones isolated, and screened for microsatellite repeats and informative microsatellite markers were developed for seven genes (GNRHR, IDUA, MAN2B2, MSX1, PDE6B, PPP2R2C, and RGS12). Three genes (LRPAP1, GPRK2L and FLJ20425) were mapped using genotyping assays developed from single nucleotide polymorphisms. Two genes were assigned as they were present in clones that contained mapped markers (HGFAC and HMX1). The resulting linkage map of pig chromosome 8 contains markers associated with 14 genes in the first 27 cM. One inversion spanning at least 3 Mb in the human genome was detected, all other differences could be explained by resolution of mapping techniques used. Fourteen of the most informative microsatellite markers in the first 27 cM of the map were genotyped across the entire MARC swine resource population, increasing the number of markers typed from 2 to 14 and more than doubling the number of genotyped animals with ovulation rate data (295 to 600). Results from the revised data set for the QTL analysis, assuming breed specific QTL alleles, indicated that the most likely position of the QTL resided at 4.85 cM on the new linkage map (F1,592 = 20.5150, genome-wide probability less than 0.015). The updated estimate of the effect of an allele substitution was -1.65 ova for the Meishan allele. The F-ratio peak was closest to markers for MAN2B2 (4.80 cM) and flanked on the other side by markers for PPP2R2C. Two positional candidate genes included in this study are MAN2B2 and RGS12. Future analyses will look for causative mutations within positional candidate genes and evaluate variation within the founding animals of the resource population.