Schematic representation of the genomic region spanning exon 14 to exon 18 of the gene encoding αs1-casein in cow and mouse. Diagonally hatched block and segment in the cow genome indicate exon 16 and a part of the downstream intron which is first duplicated in the mouse genome (pink arrow). This first duplication (yellow block) is duplicated in tandem seven times in the mouse genome (blue arrow). The green block indicates exon 15 existing only in cattle, sheep and goats. The red intronic segment (30 nucleotides) appears to be conserved between several species (cattle, mice, pigs and humans). In addition in mice, there is a 350-nucleotides insertion between exon 16.14 and 17, contributing to enlarge this genome segment, as compared with cow (3 kb vs. 2 kb).