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| Description: (a) A comparison of a short region of the gene that encodes ?-globin in laboratory mice (Mus musculus) and rats (Rattus norvegicus). Only one DNA strand is shown. Bases that are identical between the two sequences are connected by a vertical line. The ?-globin genes are similar because they are derived from the same ancestral gene, but they are not identical because each species has accumulated a few different random mutations since the divergence of their latest common ancestor. (b) The formation of these homologous ?-globin genes during evolution. An ancestral ?-globin gene was found in a rodent species that was a common ancestor to both mice and rats. This ancestral species later diverged into different species, which gave rise to modern rodent species, such as mice and rats. During this process, the ?-globin genes accumulated different random mutations, causing the DNA sequences of these two homologous genes to be slightly different.
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