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 alphas1 (CSN1S1), beta (CSN2), alphas2 (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/01, B/E, N and the new allele.
The allele differed from CSN1S1*B by a synonymous
transversion TCG->TCT in the codon corresponding to
Ser66 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 alphas1-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