EVOLUTION BY FUSION AND AMPLIFICATION - THE MURINE SP100-RS GENE-CLUSTER

Sp100 is a single-copy gene in the human and the mouse. A related gene , Sp100-rs, occurs in multiple copies and forms a conspicuous cluster in the mouse chromosome 1. Murine Sp100 and Sp100-rs are homologous fr om the promoter up to a position in intron 3, but they differ 3' of th at position. In the genus Mus, Sp100-rs is present in one phylogenetic branch, represented by the house mouse, M. musculus, but probably doe s not exist in another branch, represented by M caroli. Thus, Sp100-rs arose relatively late in the evolution of the genus Mus, whereas Sp10 0 existed in the common ancestor of the human and the mouse. The Sp100 -rs gene cluster probably evolved by gene fusion followed by amplifica tion and diversification.