Abstract presented at 2001 Annual Meeting American Society of Animal Science, Indianapolis. J. Anim. Sci. 79 (Suppl. 1):340.
Evidence of Paternally Imprinted QTL around IGF2 in a Berkshire-Yorkshire Cross
H. K. Lee1, J. C. M. Dekkers2, R. L. Fernando2 and M. F. Rothschild2
1National Livestock Research Institute
2Department of Animal Science, Iowa State University, Ames, IA 50011
A paternally imprinted QTL with major effect on muscle mass and fat deposition near IGF2 on SSC2 has been reported for crosses of the Large White with Pietrain and Wild Boar breeds. Our objective was to confirm the presence of an imprinted QTL on SSC2 in an F2 cross between the Berkshire and Yorkshire breeds. Data on average backfat (ABF) and loin-eye area (LEA) from 512 F2 animals and genotypic data for 8 markers on SSC2 were used. Breed cross regression interval mapping was implemented using the following QTL models: Mendelian (additive and dominance effects), full imprinting (allowing for different maternal and paternal allele effects plus dominance), paternal imprinting (only paternal expression), and maternal imprinting (only maternal expression). Tests of each model against the no-QTL model and tests of full imprinting against the Mendelian, paternal and maternal imprinting models were used in a decision tree to determine presence and mode of inheritance of QTL. Chromosome-wise significance thresholds were determined by permutation. Tests of the Mendelian against the no-QTL model showed no evidence of QTL for ABF and LEA (p>0.05) but tests of the full imprinting against the no-QTL model detected a QTL for both traits at the same position on the distal end of SSC2p (p<.01 for LEA and p<.02 for ABF), near IGF2. Further testing for mode of inheritance showed that the full imprinting model was not significant over paternal imprinting (p>.10) but highly significant over maternal imprinting (p<.01), indicating evidence for exclusive paternal expression. The final analysis of paternal imprinting against the no QTL model was highly significant (p<.01). Favorable alleles originated from the Yorkshire and, when transmitted through the sire, reduced average backfat by .1 cm and increased LEA by 1.0 cm2, compared to Berkshire alleles. Evidence of these QTL, which were not detected based on a Mendelian model, confirms that the IGF2 region is imprinted in pigs and harbors important QTL for muscularity and fat deposition. Supported by USDA CSREES # 00-52100-9610 and an industry consortium consisting of National Pork Producers Council, Iowa Pork Producers Association, Iowa Purebred Swine Council, Babcock Swine, Danbred USA, DEKALB Swine Breeders, PIC, Seghersgenetics USA, and Shamrock Breeders..
Keywords: QTL detection, imprinting, IGF2