progenitor gene

Richard M Kliman rkliman at runet.edu
Wed Jun 11 08:52:28 EST 1997


In article <5nlsmk$60d at news.u-strasbg.fr>,
Francois JEANMOUGIN <jeanmougin at igbmc.u-strasbg.fr> wrote:
>In article <Pine.3.89.9706061319.A541209189-0100000 at vax.cs.hscsyr.edu>,
>	higginss at VAX.CS.HSCSYR.EDU writes:
>> Greetings,
>> 
>> Would someone point me towards data or provide opinion on what gene(s) 
>> is the most ancient and which extant organisms is likely the most ancient.
>
>	Well, I will try to explain it clearly in english (quite 
>hard for me ;-). There is no ancient gene in living organism and
>there is no living organism that is the most ancient. If you
>want to find an old gene and an old organism, you have to make
>some paleontology. Extant living organism has evolved as long
>as you and me, they diverge earlier in evolution (this perhaps
>has to be said differently)>

I think this view, while more or less valid, has become something of a 
dogma.  Yes, if something is extant, it is not ancient.  However, the 
validity of the statement that all extant organisms are equally diverged 
from a common ancestor depends on the definition of "diverged."  Assuming 
a single common ancestor, then, yes, all extant organisms are equally 
diverged from the most recent common ancestor.  [This should at least 
work at the level of homologous nucleotide sites.]

However, if diverged means something else, like quantitatively different, 
then equal divergence of all extant genes from a common ancestor is not 
expected - assuming the genes have some function.  To expect this, one 
would have to assume that the original function of the gene in the 
original organism became irrelevant very quickly during evolution.  Taken 
to its ridiculous extreme, one would have to assume that genes lose their 
functional identity between generations, thus allowing them to evolve 
independently toward a new functional identity in different lineages.

>	A living organism, in all phylum, did receive the same
>amount of mutations and so the genes in their are also
>divergent from the common ancester.

Is this so?

My apology to the original poster: I'm afraid I've said nothing that will 
help you, or anyone else, identify an extant gene that is most similar to 
the first gene found in a living organism.  I'll leave it to others to 
argue about whether or not an extant organism is most similar to the 
common ancestor of all extant organisms.

Rich Kliman
Dept. of Biology
Radford University



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