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Please help!

Dom Spinella dspinella at chugaibio.com
Mon Nov 2 12:43:46 EST 1998

> Hello,
> I'm in freshman Honors Biology and we have been assigned an interesting but
> odd question for our midterm paper. We have to devise a way to use
> biotechnology to increase the genetic diversity of cheetahs. Or, if this is
> impossible, then we have to describe what is wrong with the idea and why it
> can't be used. Is there a way to use biotechnology to introduce a gene that
> is immune to a particular virus (cheetahs are very susceptible to FIP)??
> If anyone has any ideas on how to solve this problem, please help! (we are
> allowed to ask anyone's input except for someone in the class)
> Thanks,
> Ashley

Well Ashley, even if there were a way to introduce a gene into Cheetah
embryos which would confer resistance to FIP (you'd have to first figure
out what that gene might be -- not a trivial problem!), it wouldn't
really increase genetic diversity of the population would it? After all
there are tens of thousands of genes and simply adding one new
polymorphism to the population (albeit a very useful one) doesn't
appreciably change the total genetic diversity. The problem with
Cheetahs (and many other animals whose population is rapidly decreasing)
is inbreeding which results in loss of heterozygosity -- and is a step
along the road to extinction. The problem with inbreeding is that all
diploid animals (humans included) carry recessive lethal mutations in
many genetic loci.  However, each animal in a healthy outbred population
usually carries a different set of such mutations which are therefore
"sheltered" because they are paired with normal genes (which are usually
dominant) derived from the other chromosome. This is likely why diploidy
and sexual reproduction evolved in the first place -- to mitigate the
deleterious effects of mutations. Because related animals often share
the same set of lethal (or deleterious) mutations by descent, when they
interbreed the loci have increased liklihood of becoming homozygous
resulting in epression of the lethal or deleterious phenotype. 

Genetic diversity is a property of the population as a whole and it is
not really possible to increase it by introducing new genes that don't
already exist somewhere in the Cheetah population. However, it is
possible to reduce homozygosity in individual Cheetahs by preventing
inbreeding and ensuring that matings take place between different
breeding populations. It seems to me that the way to use biotechnology
in this context is to assess polymorphism (using DNA markers such as
STRs in blood or other tissue samples) in different breeding populations
of Cheetah (perhaps located in distant areas of the animals' range), and
then choose to mate pairs (perhaps by in vitro fertilization -- another
area of Biotechnology) that are most genetically disimilar -- but would
likely never have found each other on their own. The measurement of
genetic polymorphism is a an old and venerable subject of the discipline
of Population Genetics and you should begin your research by looking up
some elementary texts in this area.  Biotechnology has simply increased
the sophistication of the genetic markers that are measured, but it
hasn't changed the measurement or the statistics.

I hope this helps and good luck with your paper.

D.G. Spinella, Ph.D.

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