MOLECULAR EVOLUTION

More documents

Recommendations

Info

9. The molecular clock The integrated phylogenetic trees support the basic idea that changes in the sequences of particular genes or proteins occur at a constant rate, at least in the lineages of organisms whose generation times and overall biological characteristics are quite similar to one another. This apparent constancy in the rates at which sequences change is referred to as the molecular-clock hypothesis. Molecular clocks have a finer time resolution than the fossil record and are a more reliable guide to the detailed structure of phylogenetic trees than are classical methods of tree construction, which are based on comparisons of the morphology and development of different species. For example, the precise relationship among the great-ape and human lineages was not settled until sufficient molecularsequence data accumulated in the 1980s to produce the tree that was shown Genetica per Scienze Naturali a.a. 08-09 prof S. Presciuttini
10. Rate of molecular evolution The constant rate of neutral substitution predicts that, if the number of nucleotide differences between two species is plotted against the time since their divergence from a common ancestor, the result should be a straight line with a slope equal to μ. That is, evolution should proceed according to a molecular clock that is ticking at the rate μ. Because molecular clocks run at rates that are determined both by mutation rates and by the amount of purifying selection on particular sequences, a different calibration is required for genes replicated and repaired by different systems within cells. Most notably, clocks based on functionally unconstrained mitochondrial DNA sequences run much faster than clocks based on functionally unconstrained nuclear sequences because of the high mutation rate in mitochondria. Genetica per Scienze Naturali a.a. 08-09 prof S. Presciuttini
Page 1 and 2: MOLECULAR EVOLUTION Questo document
Page 3 and 4: 2. Similarity of nucleotide sequenc
Page 5 and 6: 4. Human and chimpanzee leptin gene
Page 7 and 8: 6. Which individual’s DNA have to
Page 9: 8. Functional Constraint Changes to
Page 13 and 14: 12. Differences among nucleotide su
Page 15: 14. Different clok rates in differe

MOLECULAR EVOLUTION

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?