Characterization of the casein gene complex in West African goats and description of a new αs1-casein polymorphism

The analysis of casein polymorphisms was carried out in West Africa goat populations: Red Sokoto ( n = 57), West African Dwarf Nigeria ( n = 27), West African Dwarf Cameroon ( n = 39), and Borno ( n = 37). The 4 casein genes alpha(s1) ( CSN1S1), beta ( CSN2), alpha(s2) ( CSN1S2), and kappa ( CSN3) were typed at the DNA level. No null alleles were found in any of the genes analyzed. A PCR single-strand conformation polymorphism method was implemented for the identification of CSN1S1*F allele simultaneously with A/0(1), B/E, N and the new allele. The allele differed from CSN1S1*B by a synonymous transversion TCG -> TCT in the codon corresponding to Ser(66) of the mature protein. The new allele, named CSN1S1*B', occurred at a high frequency in all the populations, ranging from 0.295 ( West African Dwarf Cameroon) to 0.405 ( Borno). A greater frequency was found for alleles associated with high alpha(s1)-casein quantity, as has already been observed in the goat populations from the Mediterranean area. The intermediate E allele occurred only in the Red Sokoto and at a low frequency. The faint F allele occurred in 3 populations at frequencies lower than 0.03. Linkage disequilibrium occurred in all the populations, with highly significant differences in Borno, Red Sokoto, and West Africa Dwarf Nigeria, and significant differences in West Africa Dwarf Cameroon. Only 10 haplotypes showed frequencies >= 0.05 in at least 1 of the 4 populations considered, and the overall frequency was > 0.1 only for 4 haplotypes: BAAB, B'ACA, ACAB, and BACA ( in the order CSN1S1-CSN2-CSN1S2-CSN3). Haplotype BAAB, postulated as an ancestral haplotype in previous studies, was the most common haplotype in all breeds except Borno, where B'ACA was predominant. The results obtained are of considerable significance given that very little information exists on the subject for African goats. The high frequency of strong alleles in the calcium-sensitive caseins as well as the high linkage disequilibrium found among the casein genes in the African breeds analyzed may suggest that specific casein haplotypes have already been selected due to their advantages for nutrition. Haplotypes providing greater protein and casein content would increase the energy content of milk, thus resulting in more favorable growth and survival of young goats and humans consuming the milk.