definition of Orthologues, Homologues, etc

William R.Pearson wrp at alpha0.bioch.virginia.edu
Mon Oct 9 12:31:45 EST 2000


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).

There are two subclasses of homologs - orthologs and paralogs.
Orthologs are the same gene (e.g. cytochome 'c'), in different
species.  Two genes in the same organism cannot be orthologs.
Paralogs are the results of gene duplication (e.g. hemoglobin beta and
delta).  If two genes/proteins are homologous and in the same
organism, they are paralogs.

Bill Pearson








More information about the Mol-evol mailing list