definition of Orthologues, Homologues, etc

Mike Syvanen syvanen at ucdavis.edu
Mon Oct 9 18:59:47 EST 2000

"William R. Pearson" wrote:

> Holger Hupfer <hupfer at botanik.biologie.uni-muenchen.de> writes:
> > I am a little worried about the classifications of genes or proteins.
> > What is the Difference between orthologues, homologues or analogues? Can
> > anyone help me with this?
> Homologs refer to proteins that share a common ancestor.  Analogs (a
> term that is rarely used), do not share a common ancestor, but have
> some functional (rather than structural) similarity that causes them
> to be included in a class (e.g. trypsin like serine proteinases and
> subtilisin's are clearly not related - their structures out side the
> active site are completely different, but they have virtually
> geometrically identical active sites and thus are considered an
> example of convergent evolution to analogs).

unless, of course, the active sites of trypsin and subtilisin are
homologous and that they have subsequently fused to other
nonhomologous proteins to produce today's members.

Mike Syvanen


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