>At 1:14 PM 8/22/96, CurtAdams@aol.com wrote:
>>The robustness is not well-established but is suspected; eukaryotes have as
>>much variation in their rRNAs as prokaryotes. It should be very hard to
>>generate that much variation without an enormous amount of time.
>What if the key sequence of mutations developed in a prokaryote that gave
>rise to what is now the eukaryotic cell-plasm, but that various descendants
>of this "swallower" prokaryote then adopted a large number of different
>prokaryotes as proto-nuclei? Is it possible that multiple independent
>origins (perhaps thousands or millions, once the essential "swallowing"
>mutations had developed) could account for the observed variation in
>eukaryotic rRNAs?
Yes, it's possible. Current thought is that it would be very difficult to
mix rRNA from different lines into one functional ribosome. However,
evolution of rRNAs is ill-understood.
>If the idea of multiple independent origins is correct, then I think we'd
>*expect* to see as much variation among eukaryotes as we see among
>prokaryotes, even if the eukaryotes have only existed for a much shorter
>time, because eukaryotic genes would arise from a broad sampling of
>prokaryotic genes.
As I understand it, not only is there a lot of variation within eukaryotes,
but eukaryotes as a group differ substantially from prokaryotes. Multiple
origins should leave most eukaryotes more closely related to their
prokaryotic relatives than their eukaryotic non-relatives, but that isn't the
case.