Genetic polymorphism of milk proteins in African Bos taurus and Bos indicus populations. Characterization of variants alpha(s1)-Cn H and kappa-Cn J

The polymorphism of caseins, cr-lactalbumin and beta-lactoglobulin Nas inve stigated in African Bos taurus (N'Dama, Baoule, Kuri) and Bos indicus (Shuw a Arab, Sudanese Fulani) populations. The respective frequencies of alleles alpha(s1)-Cn(B) and alpha(s1)-Cn(C) in the N'Dama (0.89 and 0.11) and Baou le (0.92 and 0.08) breeds were almost opposite to those found in the Shuwa Arab zebu (0.22 and 0.78), a true zebu, which confirms a phenomenon already documented in the literature. Because the alpha(s1)-Cn(B), beta-Cn(A1), ka ppa-Cn(B) haplotype was strongly predominant in N'Dama and Baoule (0.56 and 0.60), as compared to the alpha(s1)-Cn(C), beta-Cn(A2), kappa-Cn(A) haplot ype in the Shuwa Arab zebu (0.63), an opposite trend in frequencies was als o observed between taurines and zebus at the beta-Cn and kappa-Cn loci. The se results confirm that the polymorphism of caseins provides an efficient m arker system to discriminate Bos taurus from Bos indicus origins. The Kuri was at an intermediate position, since, in this population, the alpha(s1)-C n(B) allele predominated as in taurines, while the alpha(s1)-Cn(C), beta-Cn (A2), kappa-Cn(A) haplotype was the most frequent, as in zebus. This may be interpreted as revealing intercrossings with zebus in the previous history of this cattle type. Conversely, but to a lesser degree, the polymorphism of the Sudanese Fulani zebu indicates a taurine influence, in accordance wi th what is accepted about the origins of this cattle type. No polymorphism of alpha(s2)-casein could be identified, while a-lactalbumin was polymorphi c in all populations. Two additional variants, probably specific to African cattle, were observed. Variant I-I of a,l-casein, found in Kuri, is charac terized by the deletion of the eight amino acid residues (51-58) coded by e xon 8, a probable consequence of exon skipping. Allele alpha(s1)-Cn(H) is d erived from allele alpha(s1)-Cn(B). Variant J of kappa-casein, found in Bao ule, is derived from variant B by the substitution of Ser 155 (B) --> Arg ( J). The existence of at least another allele of alpha(s1)-casein was sugges ted. (C) Inra/Elsevier, Paris.