Polar overdominant inheritance of a DLK1 polymorphism is associated with growth and fatness in pigs.

The polar overdominance model of inheritance was proposed to explain the non-Mendelian expression of callipyge muscular hypertrophy in sheep. The callipyge locus (CLPG) maps to the distal portion of ovine Chromosome 18 within the DLK1- GTL2 region and corresponds to human Chromosome 14q32, where uniparental disomy (UPD) of the region is associated with multiple congenital anomalies, including growth retardation and obesity. We investigated the porcine DLK1- GTL2 region in a cross of two pig breeds to determine if the callipyge polar overdominance is present in another species. Analyses of the parental origin of DLK1 polymorphism in the F2 offspring found that paternal inheritance of DLK1 allele 2 and maternal inheritance of the allele 1 was significantly associated with decreased fat deposition and increased lean muscle mass, while the opposite parental inheritance of these alleles was associated with slower prenatal and postnatal growth. These results suggest that the polar overdominance mode of inheritance is present in the pig chromosomal region that is homologous to the CLPG locus in sheep. Further study in pigs can provide important insights into understanding the molecular regulation of imprinted genes that are associated with human UPD14 and sheep callipyge phenotypes.