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Transcript of Phylogenetic Relationships
Although there is a detailed fossil record of Equids, there are still many controversial issues surrounding equid relationships, not least in the living species.There have been a few studies of the evolution of Equus using biochemical data. The most recent, by Ishida et al. , was the first to use DNA sequence information. The a1, a2, and u genes of donkey (E. asinus), onager (E. hemionus),plains zebra (E. burchelli), Grevy’s zebra (E. grevyi), and mountain zebra (E. zebra) were amplified and sequenced in both directions. Phylogenetic analysis using the neighbor-joining and maximum likelihood methods were carried out with the PHYLIP package. Data was collected and compared. Trees were constructed using a and u data both separately and together. Divergence times were calculated with the equation T 4 K/2r Methods Results Despite the considerable similarities between the genes (within the homology block a1 and a2 genes within each species are all at least98.5% identical, the a1 genes compared between species are at least 97% identical, and the a2 genes at least 98% identical between species), a number of differences are observed between both paralogous and orthologous genes. Discussion By E. Ann Oakenfull,* John B. Clegg
Institute of Molecular Medicine, University of Oxford, Oxford, UK
Received: 22 April 1997 / Accepted: 20 July 1998 Horses diverged from the zebra/ass ancestor ~2.4 million years ago
the zebra and ass species arose in a rapid radiation ~0.9 million years ago.
The relationships between the zebras and the asses cannot be distinguished clearly with either method *The distances used for estimating the divergence time were based on noncoding and third codon positions in the a genes only. Introduction *all images are directly from article