Legislation/Policy Issue surrounding Genetic Tests

Joe Felsenstein joe at GENETICS.WASHINGTON.EDU
Tue Sep 25 14:41:20 EST 1990


Antony Courtney's "gray area" makes an assumption, one that is bigger than
one might think.  He states one of the main arguments for incentives for
reproduction of

>                                                   parents whose genetic
> profiles indicate their children will be healthy

as being that it would discourage people with "unhealthy" genes not to
reproduce,

>                                  hence removing such "inferior" genes from the
> gene pool.

It seems as if this should have a large effect, but actually it would in most
cases have such a small effect (even if the incentives worked) that the
advantage is likely to be trivial.

If a mutant allele is strongly deleterious it will not be passed on to
future generations anyway, whether or not the individuals are born.  If it is
recessive, only a tiny fraction of all copies of the gene are in affected
individuals, and if they are eliminated there is only a small change per
generation in the gene frequency (for example, only about 1% of copies of
the cystic fibrosis allele are contained in affected individuals).  The cases
in which a substantial effect could be obtained would be dominant genes of
small effect on fitness but large social cost of the affected individual
(Huntington's disease comes to mind).  There are not too many of these kinds
of genes that I know of.

Thus even in the unlikely event that such a policy would (a) be introduced
and (b) affect reproductive patterns, it would have a rather small effect
on healthiness of future generations.  I can think of better uses for the
money.

There is a population genetics literature on the related question of whether
curing genetic disorders will lead to a rapidly rising tide of cases.  It
won't:

Crow, J.F.  1966.  The quality of people: human evolutionary changes.
   Bioscience  863-867.
Motulsky, A.G., G.R. Fraser, and J. Felsenstein.  1971.  Public health and
   long-term genetic implications of intrauterine diagnosis and selective
   abortion.  Birth Defects -- Original Article Series  vol. 7, no. 5, pages
   22-32.

----
Joe Felsenstein, Dept. of Genetics, Univ. of Washington, Seattle, WA 98195
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