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What is a Quagga?
Interpreting the Phylogenetic Trees and Assessing the Relatives of the Quagga
We can make the following conclusions about the relationship of the quagga and its evolutionary age from the trees.
Tree Topology The trees estimated for both the co1 and nd1 gene regions had the same topology. In these trees the quagga is most closely related to the Plains zebra (Equus burchelli). Its next closest relative is the Mountain zebra (Equus zebra). The quagga is only distantly related to the horse (Equus caballus). The tree also indicates that the two species of zebra are more closely related to one another than either is to the horse. And so, the zebras form a group which contains the quagga. From this we can conclude that the quagga is a zebra and not a horse.
When we look at the untransformed trees below, we see that the amount of evolutionary change has been slightly different in the two genes. The tree obtained from the co1 region (left) shows that the branches separating the quagga and the Plains zebra are about half the length of the branches separating the quagga and the Mountain zebra. Perhaps the common ancestor of the Plains zebra and quagga is half as old as the common ancestor of the whole zebra group.
The tree obtained using nd1 is harder to read. It suggests that the quagga arose a relatively long time ago, shortly after the common ancestor of the two species of zebras.
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