35-bp deletion in ABCG2 gene: mini-review and report on two herds of Bulgarian dairy synthetic population sheep breed

A mutation in the ovine ABCG2 gene could influence the fat content and milk yield in sheep. The aim of this study was to identify a 35-bp deletion/insertion in intron 5 of the ABCG2 gene in two herds of the Bulgarian Dairy Synthetic Population (BDSP) breed. The first population was raised in the Agricultural Institute in Shumen and included 116 ewes. The second one was bred at the Institute of Animal Science - Kostinbrod and included 68 ewes. Genomic DNA was extracted from a total of 184 blood samples. The allelic variants were determined by polymerase chain reaction (PCR) amplification with a specific primer set. The results revealed the presence of the wild-type allele "+" with a frequency of 0.53 and the mutant allele "-" with a frequency of 0.47 in BDSP - Shumen. In the animals from BDSP - Kostinbrod, the wild-type allele "+" had a frequency of 0.71 and the mutant allele "-", a frequency of 0.29. All three possible genotypes were identified in both herds. In BDSP ewes - Shumen, the wild-type genotype "+/+" had a frequency of 0.22; the heterozygous genotype, a frequency of 0.63; and the mutant genotype "-/-", a frequency of 0.15. In BDSP - Kostinbrod, the wild-type genotype "+/+" had a frequency of 0.55, the heterozygous genotype "+/-", 0.32; and the mutant genotype "-/-", 0.13. Both tested herds were not consistent with the Hardy-Weinberg equilibrium (HWE). In BDSP - Shumen p = 0.01 and in BDSP - Kostinbrod p = 0.05.