definition of Orthologues, Homologues, etc
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.
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
vocabulary? I am not sure they can.
More information about the Mol-evol