Phylogenetic relationships within the genus Equus and the evolution of alpha and theta globin genes

Sequences of the alpha 1, alpha 2 and theta globin genes from six squid spe cies have been determined to investigate relationships within the genus Equ us. Analyses using standard phylogenetic methods, or an approach designed t o account for the effects of gene conversion between the alpha genes, gave broadly similar results and show that the horses diverged from the zebra/as s ancestor similar to 2.4 million years ago and that the zebra and ass spec ies arose in a rapid radiation similar to 0.9 million years ago. These resu lts from the ct genes are corroborated by theta gene data and are in contra st to mitochondrial DNA studies of the phylogeny of this genus, which sugge st a more gradual set of speciation events.