The scope of this study was to identify sequence polymorphisms in the β-1,4- galactosyltransferase-I gene (B4GALT1), the gene which encodes the catalytic part of lactose synthase enzyme. Exons of the gene were scanned for the presence of allelic variation among a sample of 400 Iranian Holsteins, using the single strand conformation polymorphism technique followed by sequencing. Nine polymorphic nucleotide sites and 16 different genotypes of B4GALT1 were identified. We concluded therefore that the β-1,4-galactosyltransferase-I gene was polymorphic in Holsteins. Considering the biological roles of the B4GALT1 gene, we suggest that further studies are critical to investigate the biological effects of the SNPs reported in this study

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