Archetype » Postmodernism http://roberto.kellerperez.com Ant reconstruction one homology at a time Tue, 21 Dec 2010 16:19:12 +0000 en hourly 1 http://wordpress.org/?v=3.2.1 Homology Weekly: DNA http://roberto.kellerperez.com/2009/04/homology-weekly-dna/ http://roberto.kellerperez.com/2009/04/homology-weekly-dna/#comments Wed, 01 Apr 2009 11:27:13 +0000 Roberto Keller http://roberto.kellerperez.com/?p=681 dnaAt any given position along their DNA sequences, ants may have any of the following four nucleic acid types: A, T, C or G. Unless we are dealing with the mitochondrial genome that is known to have quite a few A+T-rich regions in insects, in which case expect to find just those two types of nucleotides.

One problem, though, is that in order to determine the correct correspondence between single positions on different species, that is, in order to align the sequences we need information about what nucleotides are to the left and right of the position of interest1. The same has to be done for those flanking positions as well, simultaneously. And since species are related by common ancestry as a result of a process of divergent evolution, they have to be compared within a tree-shaped phylogenetic framework. So it is best if we align sequences at the same time that we search for the phylogenetic trees.

That is all one really needs to know. The remaining positions in the DNA sequence are just serial homologues.

Note

  1. This is just Etienne Geoffroy Saint-Hilaire (1772–1844) ‘principe des connexion’. ↩
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