Phylogenetic relationships within the genus Equus and the evolution of α and θ globin genes

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