[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: "Common ancestor" in cladistics


Christopher Taylor wrote:

Many genes are present in multiple copies in a single genome (ribosomal
genes, for instance), and each of those copies may have its own evolutionary
history. If phylogenies are constructed using sequences that actually come
from a mixture of copies from different species, the resulting tree will be
quite different from the 'true' tree.

I understand this, yes. What you're talking about is 'orthologous' versus 'paralogous' genes. Unless this distinction is recognized for a given sample of apparently homologous genes, you can end up with all sorts of weird phylogenies.


    And as a final pointer, ribosomal genes have generally been used in
prokaryotic phylogentics because it was imagined that they are so vital and
integral to the function of the organism that lateral transfer was not
possible, but some researchers now suspect that this is not necessarily the
case. The hyperthermophilic eubacteria Thermotoga and Aquifex, for example,
which appear quite close to Archaebacteria in rDNA trees, may do so because
they've picked up genes from Archaebacteria - non-ribosomal genes often put
them much higher among the eubacteria (Cavalier-Smith, 2002, in the IJSEM).

It just so happens I've been looking at the genes of _Aquifex_ very, very recently. :-) Like all bacteria (and archaea) they are living Meccano sets when it comes to genes. I could write a whole lot more about this, but I've just remembered this is a dinosaur list....

_________________________________________________________________
Planning a family vacation? Check out the MSN Family Travel guide! http://dollar.msn.com