Molecular characterisation of k-casein gene in Girgentana dairy goat breed and identification of two new alleles

The k-casein fraction plays an important role in the formation, stabilisation and aggregation on casein micelles and thus affects technological and nutritional properties of milk. In this study, exon 4 of k-casein (CSN3) gene was sequenced and analysed in Girgentana goat breed. Analyses of the obtained sequences showed the presence of A, B, D, and G known alleles and two new genetic variants, named D’ and N. The new D’ allele differs from D in one transition, G284→A284, which did not cause amino acid change. The new N allele differs from A in five single nucleotide polymorphisms (SNPs): T245/C245, G284/A284, G309/A309, G471/A471 and T591/C591, while it differs from C in one transition, i.e. T583→C583. Comparing the amino acid sequences of N and A alleles, the first two SNPs caused no amino acid change, whereas the other SNPs produced changes (Val65/Ile65, Val119/Ile119, and Ser159/Pro159, respectively). Comparison of N allele with C revealed theamino acid change Val156→Ala156. The most frequent allele was A (0.480) followed by B (0.363), D (0.112), and N (0.034). The D’ and G alleles were identified only in two animals and in heterozygous conditions with a very low frequency (0.005). The most common genotype was AB (39.5%) followed by AA (19.5%), AD (12.7%), and BB (11.7%). Homozygous D’D’, GG, and NN individuals were not found. Further analysis will be performed in order to establish associations among genotypes and quantitative and qualitative milk traits.