Tuesday, March 8, 2011

Redefining Evolutionary Relationships

The evolutionary tree of life may undergo a makeover in the next decade or so.

In the past, the primary sources of information about the evolutionary relationships between organisms came from the fossil record or from comparative anatomy, physiology, or biochemistry. But now a new scientific field called phylogenomics (the study of the evolutionary history of organisms based on genetics) has emerged, thanks to the increased availability and cheap cost of sequencing DNA.

How does comparative DNA sequence data tell us anything? By tracing specific differences in the nucleotide sequences of the genes of closely related species, phylogeneticists can tell just how closely related two species are and when they most likely split from a common ancestor. That’s because when a mutation (a change in nucleotide sequence) occurs by random chance in a common ancestor, that mutation should still be present in all subsequent descendants of that ancestor. So when exactly the same mutation appears in the same gene in two species, the mutation most likely occurred before the two species split from a common ancestor – i.e. the two species are related to each other by a common ancestor.

The DNA sequences of a wide variety of species are now known, and more are being determined every day. We can expect challenges to the current tree of life (also called the phylogenetic tree) as the data are analyzed and debated.

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