definition of Orthologues, Homologues, etc

Mike Syvanen syvanen at ucdavis.edu
Thu Oct 12 14:28:38 EST 2000



James McInerney wrote:

> Bill mentioned Richard Owen, the first director of the Natural History
> Museum (formerly, British Museum of Natural History) and the fact that
> he coined the word "homologue".
>
> His definition was that it was "the same organ under every variety of
> form and function".  This will extend to molecular sequences very nicely
> - two amino acid positions are homologues if they are the 'same organ',
> not an analagous organ.  Two proteins are the 'same organ' if they are
> derived from a common ancestor.
>
> I don't believe the original definition would have allowed for the lower
> jaw and the kidneys to be considered homologous, even though it can be
> argued that they must have sometime derived from common stock.  In the
> same way only those protein sequences that really are the 'same organ'
> could be considered homologous.
>
> James

Molecular evolutionists accept parology as an example of homolgy. This
fact has overwhelmed Owen's definition of homology.  There are just
too many different proteins that clearly evolved from a common ancestral
form.  The term orthology is in the process of replacing Owen's homology.

This dispute arises from an old problem biologists have been debating since
Darwin:  Can systematists, whose goal is classification and evolutionary
biologists, whose goal is reconstructing evolutionary histories, share the
same
vocabulary?   I am not sure they can.

Mike Syvanen




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