Mary K. Kuhner mkkuhner at phylo.genetics.washington.edu
Fri Sep 8 12:26:53 EST 1995

In article <42ot1c$9r1 at newsbf02.news.aol.com> tz68 at aol.com (TZ68) writes:
>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

What generally happens is that a gene is duplicated (due to errors in 
chromosome replication or recombination).  At this point there are two
functional, identical copies.  However, there is no pressure to keep
both copies working, since the organism can get by with just one, so
mutations tend to accumulate and eventually one copy is likely to stop
working.  (Alternatively, it may change to having a new function--this
is thought to be a major way that new genes come into being.)  At this
point it is a pseudogene.  It will continue to accumulate mutations
until it is so beat-up we can't recognize it anymore, or until it
acquires some useful function by chance.

The possibility of evolving a new function is a "value" a pseudogene
might have.  DNA which is almost the same as a functional gene is much
more likely to become, by chance, a functional gene than random DNA is.

How fast a duplicate copy becomes a pseudogene depends on the local
mutation rate, on chance, and on whether having the extra copy is
irrelevant, slightly bad, or slightly good for the organism.  Creation
and loss of pseudogenes is an ongoing process.  There are lots of good
examples known in higher primates, especially in the histocompatibility
and hemoglobin gene families.

Mary Kuhner mkkuhner at genetics.washington.edu
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