Potential status of A1 and A2 variants of bovine beta-casein gene in milk samples of Indian cattle breeds

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Abstract
This study aimed to determine the polymorphism in 7th exon of beta-casein gene (CSN2) gene in seven domestic (Kosali, Tharparkar, Gangatiri, Sahiwal, Gir, Khariar, Motu) and two exotic cattle breeds (Jersey and Holstein-Friesian). Genomic DNA was extracted from 1000 milk samples, and the C > A polymorphism in CSN2 was determined using the tetra-primer amplification refractory mutation system-polymerase chain reaction method. In all Indigenous cattle breeds, the mean frequency of A1A2 and A2A2 genotypes was 0.19 and 0.80, respectively. The A1A1 genotype was absent in all seven domestic cattle breeds. The frequency of the A2A2 genotype was highest in the Gir breed (0.93). However, the Sahiwal, Tharparkar, and Motu breeds also had a higher frequency of A2A2 genotype compared to other breeds. In contrast, Gangatiri breed of India showed lowest frequency of A2A2 genotype. The mean A1 and A2 allele frequency was 0.09 and 0.91, respectively. In exotic breeds, the mean frequencies of the A1A1, A1A2, and A2A2 genotypes were 0.42, 0.55, and 0.03, respectively. Similarly, the mean A1 and A2 allele frequency was 0.69 and 0.31, respectively. This study suggests the high potential of Gir, Sahiwal, Tharparkar, and Motu cattle for A2 milk production since they carry a favorable A2 genotype.

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