Figure 4.

(A) A postulated schema for the origin of feline DR subregion evolution by gene duplication (dup1, dup2, dup3, dup4), inversion (In 1) and pseudogene transpositions. Consider the primitive ancestral occurrence of two DR units: one DRB and one DRA gene arranged in a tail-to-tail fashion on a 30-kb segment. Genes within this unit underwent two successive early gene duplications (dup1 and dup2) followed by a third duplication of the AB unit (dup3). A fourth pseudogene DRB duplication (dup4) punctuated by three pseudogene transposition/insertions from disperse autosomal coding loci would account for the disposition and orientation of the DRA and DRB gene family, at least for the presently observed haplotype as illustrated in B. (B) Present gene order and orientation of DR genes of the cat. The bars indicate percent nucleotide sequence identity of connected gene sequences. The 97%–98% similarity of the internal B–A blocks indicates that dup3 was relatively recent.