Abstract
The genetic polymorphism of the alpha S1-casein (CSN1S1) was investigated in five sheep breeds reared in Bulgaria: Sofia (Elin-Pelin, SEPL), Copper-Red Shumen (CRSH), Local Karnobat (LKNB), Pleven Blackhead (PLBH), and Stara Zagora (STZG) sheep with an aim to establish the possible effect of a particular genotype on ovine milk composition. Based on nucleotide variation in exon III of the CSN1S1gene, two genetic variants (A and C) and three genotypes (AA, AC, and CC) have been identified using PCR-RFLP analysis on a total of 217 unrelated ewes. The allele frequencies determined a prevalence of the allele C (0.886) over the allele A (0.114) across the studied sheep populations. The homozygous CC genotype was observed in nearly 80% of the studied ewes. The calculated values for observed (Ho = 0.548) and expected (He = 0.468) heterozygosity at CSN1S1 locus indicated a relatively high degree of genetic variability in the Sofia sheep population. The greatest Nei's genetic distance (DA = 0.080) was found between the populations STZG and SEPL, while the closest relationship was established (DA = 0.000) between PLBH and CRSH, also between STZG and CRSH. The results of the association analysis indicated that CSN1S1 AC genotype was significantly associated (P < 0.05) with the highest percentages of the fat, protein, casein, solids-nonfat and total solids in Sofia sheep ewes. The genotype CSN1S1 CC was associated with the highest noncasein protein percentage, while the genotype AA was linked with the highest lactose percentage. The CSN1S1genotype did not show a significant effect (P > 0.05) in the Sofia sheep population in relation to the renneting time. In conclusion, the established single nucleotide polymorphism in the CSN1S1 locus could be used as a potential genetic marker for ovine milk composition traits, as well as for developing an effective conservation strategy towards traditional sheep breeds in the country.
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