Анотация: Due to the functions that estrogens play in the regulation of reproduction, development of mammary gland, growth and differentiation of cells, estrogen receptors and their genes are considered candidates for molecular markers of production and functional traits in farm animals. In this study, using the SSCP and DNA sequencing, we found a novel single nucleotide polymorphism (SNP) in the coding region of the estrogen receptor alpha (ER alpha) gene - the A/C transversion at position 323,396 (relative to the start of transcription site), in exon 7, that could be also detected with RFLP-CfrI. This mutation causes the amino acid replacement - Asparatic acid/Alanine in the ligand-binding domain (LBD) of the receptor