Duplication polymorphisms in exon 4 of κ-casein gene in yak breeds/populations.

The objective of this study was to compare 12 bp-duplication polymorphisms in exon 4 of the κ-casein gene among 3 breeds/populations of yak (Bos grunniens). Genomic DNA was extracted from yak blood or muscle samples (N = 211) and a partial sequence of exon 4 of κ-casein gene was amplified by polymerase chain reaction. A polyacrylamide gel electrophoresis assay of the products (169 bp) revealed 2 variants. These variants differed in a 12-bp duplication of the nucleotide sequence corresponding to amino acids 147-150 (Glu-Ala-Ser-Pro) or 148-151 (Ala-Ser-Pro-Glu). The genotype frequency and gene frequency of the 2 κ-casein variants differed among the 3 yak breeds/populations. The long form of the κ-casein gene was the predominant allele, and the Jiulong yak showed the highest frequency of the short form variant of the κ-casein gene. In addition, 2 nucleotide differences resulting in amino acid substitutions were also identified in yaks. These results are significant for designing a breeding strategy to improve the genetic makeup of yak herds.