Associations between single nucleotide polymorphisms of GDF9 and BMP15 genes and litter size in two dairy sheep breeds of Greece

The aim of the present study was to assess the presence of single nucleotide polymorphisms (SNPs) in the Growth Differentiating Factor 9 (GDF9) and Bone Morphogenetic Protein 15 (BMP15) genes, in two Greek sheep breeds i.e. Chios and Karagouniki, with high and moderate litter size (LS) i.e. number of lambs born, respectively. An examination of association(s) between the polymorphisms and LS, within breeds, was also conducted. Blood samples from 92 Chios and 96 Karagouniki ewes were collected, while repeated records on LS, were also available (n = 239 and 259, respectively). Detection of SNPs was performed on the DNA products by PCR-RLFP analysis. Data analysis included examination of allelic and genotypic differentiation between the breeds, testing for Hardy-Weinberg Equilibrium (HWE) and association analysis between polymorphisms and LS. Genetic analysis showed that the G1 and G8 mutations of the GDF9 gene were significantly over-presented only in the highly prolific breed (Chios). The B4 mutation of the BMP15 gene was significantly over-presented only in the low prolific breed (Karagouniki). Both breeds were in Hardy-Weinberg disequilibrium (HWD), possibly due to selection pressure, population sub-structure and genetic drift. Certain polymorphisms of the G1, G4 and G8 sites of the GDF9 gene in the Chios breed were found to show heterozygote advantage with no evidence of infertility for the homozygous females. A similar trend was observed in the BMP15 gene although at no statistically significant level. In the Karagouniki breed, no significant associations between the studied polymorphisms and LS were detected.