Figure 6

The distribution of A3 Z domains in mammals. The common ancestor of the indicated placental mammals was inferred to have a Z1-Z2-Z3 A3 gene repertoire. Z1, Z2 and Z3 domains are colored green, orange and blue, respectively. A question mark specifies the original AID-like ancestor. An asterisk indicates the likely period in which the bulk of the primate A3 gene expansion occurred (see main text, Figure 7 and Additional File 7). Some humans are A3B deficient (minor allele; [75]). The boxed A3 Z domain repertoires constitute the minimal set inferred from incomplete genomic sequences and EST data (Additional File 3).