B-lactoglobulin (Coded by the B-lg gene) is the major milk whey protein in ruminants. Studies have shown that this protein is polymorphic in many breeds of sheep as a result of a single base pair substitution in the B-lg gene that also gives rise to RsaI restriction fragment length polymorphism (RFLP). Blood samples were collected from 391 animals belonging to 5 Iranian and 6 Russian sheep breeds. BLg5 and BLg3 primers amplified a 452 bp fragment from exon II of the ovine B-lg gene. RsaI enzyme was used for restriction analysis of PCR products. Overall, the frequency of alleles A and B in the studied breeds were stimated as 0.65 and 0.35, respectively. The genotype BB was not seen in the Iranian and Russian Karakul, except in the Afshari and Finnish Landrace, other populations were in the Hardy-Weinberg equilibrium.

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