Pseudogenes

R M Bernstein ralph at ccit.arizona.edu
Sat Sep 9 12:48:54 EST 1995


In Article <42ot1c$9r1 at newsbf02.news.aol.com>, tz68 at aol.com (TZ68) wrote:
>Do pseudogenes arise from recent or ancient events?  Does one arise from a
>functional gene and can a functional gene arise from a pseudogene?  What
>value are pseudogenes?
>
>Just Curious

hmm, you have received quite a few posting already that really give nice
defs of pseudogenes.  although, i can add 1 or 2 examples/clarifications.  

    a)on the idea that if a gene that was duplicated, and then is a
pseudogene, and then is now functional-and that this gene is no longer a
pseudogene..(whew) i agree that its probably not a pseudogene any more, per
se, as it is now functional in some way.  although, i think that a
pseudogene has to be _un_functional for some time, and clearly duplicated
genes that mutate to having new functions are still functional-so it is not
really clear if those genes were ever really pseudogenes at all.  the
example that comes to mind is the lysozyme gene in ruminants.  this is a
gene that, through its duplication, has allowed for life as we know it.  it
was duplicated in ruminants and the duplicated gene was mutated to withstand
higher ph, etc.  that is the lysozyme in ruminants that processes cellulose
in their numerous stomachs.  they have a normal lysozyme that retains it
"original" function.  so was this gene ever a pseudo gene?  prob not, just a
duplicated gene.  (it allows "life as we know it" because out society is
based largely on the secondary or tertiary consumer abilities of the
ruminants, -kind of a social commentary)

    b) so, youre thinking , "ralph, why bring that up at all?"  because
there _are_ pseudogenes that are non-functional, ie not expressed, that are
used and are important to the fitness of an organism...namely the VH genes
in the rabbit.  they have 1 functional VH gene, meaning 1 gene that is
expressed.  thay have , oh i dont know, maybe 15-20 (or more) other VH's
that are the result of a probable duplication, that are all pseudogenes. 
never expressed!  but, thru a process known as gene conversion
(inotherwords-a miracle happened) the rabbits recombine or otherwise swap
out their expressed VH gene for either: one of the pseudo-VHs or: a piece of
one of the pseudo VHs.  and this produces the incredible diversity (also
with somatic mut, etc) that we see in the rabbit antibody repitoire!  

    c)so, the concept of a pseudogene, and mixing it up with a merely
duplicated gene has been blended together in these explanations.  i hope i
have given nifty examples to clear some of it up?

regards  ralph

Ralph M. Bernstein
Dept of Micro/Immuno
University of Arizona
Ph: 602 626 2585
Fx: 602 626 2100
url: http://lamprey.medmicro.arizona.edu



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