MOLECULAR EVOLUTION

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3. Reconstructing extinct gene sequences For closely related organisms such as humans and chimpanzees, it is possible to reconstruct the gene sequences of the extinct, last common ancestor of the two species. The close similarity between human and chimpanzee genes is mainly due to the short time that has been available for the accumulation of mutations in the two diverging lineages, rather than to functional constraints that have kept the sequences the same. Evidence for this view comes from the observation that even DNA sequences whose nucleotide order is functionally unconstrained — such as the third position of “synonymous” codons — are nearly identical. Genetica per Scienze Naturali a.a. 08-09 prof S. Presciuttini
4. Human and chimpanzee leptin genes Leptin is a hormone that regulates food intake and energy utilization in response to the adequacy of fat reserves. For convenience, only the first 300 nucleotides of the leptin coding sequences are given. Only 5 codons (of 441 nucleotides total) differ between these two sequences, and in only one does the encoded amino acid differ. The corresponding sequence in the gorilla is also indicated. In two cases, the gorilla sequence agrees with the human sequence, while in three cases it agrees with the chimpanzee sequence. Genetica per Scienze Naturali a.a. 08-09 prof S. Presciuttini
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Page 3: 2. Similarity of nucleotide sequenc
Page 7 and 8: 6. Which individual’s DNA have to
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MOLECULAR EVOLUTION

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