The goat calcium-sensitive caseins (αs1, β and αs2) represent, over many years, an excellent model for demonstrating that the major part of the variability observed in the content of these proteins in goat milk is mostly due to the presence of autosomal alleles at single structural loci (CSN1S1, CSN2 and CSN1S2 respectively) clustered on a 200 kb segment of chromosome 6; furthermore, CSN1S1 and CSN2 are convergently transcribed and are only 12 kb apart (Rijnkels, 2002).

Alpha-lactalbumin (α-la), a calcium metalloprotein, is one of the major serum-proteins in ruminant milk (Jenness, 1982) and induces lactose synthesis in the mammary gland by interacting with the enzyme UDP-galactosyltransferase, giving rise to the heterodimer enzyme lactose synthase (Ebner & Brodbeck, 1968; Kuhn, 1983). The goat α-la transcription unit (LALBA), located on chromosome 5 (Hayes et al. 1993), is organized in 4 exons varying in length from 75 nucleotides (3rd exon) to 329 nucleotides (4th exon) coding for a 123-amino acid polypeptide chain (Vilotte et al. 1991). According to the strong similarity between bovine α-la (Vilotte et al. 1987) and human lysozyme (similar molecular weight, the same number of S-S bonds, identical N and C terminal residues; Peters et al. 1989), it has been proposed that both genes arose from a common ancestor (Vilotte et al. 1991).