[ExI] biology term

[rex]

spike <spike66 at att.net> [2016-10-11 22:26]:
> 
> 
> When a mutation is recessive and each parent carries one copy, there is
> about a 25% chance the offspring will inherit both copies of the mutation.
> In the case of a lot of genetic diseases, if either copy is the
> non-mutation, then the disease is not expressed.  So if two carriers of that
> mutation mate, then the offspring have about a 50% chance of being a carrier
> and about a 25% chance of being free entirely of the mutation.
> 
> In the case of Tay-Sachs disease, it is known that some populations (such as
> Ashkenazi) have a number of carriers, so the Jewish couples have a known
> risk of suffering the heartbreak of a Tay-Sachs baby, who will not survive
> to bring them grandchildren.  
> 
> Given that a mutation is detrimental in some cases, why does that mutation
> survive in a population?  A theory that Lee Corbin and I kicked around is
> that in every case where a mutation carries the risk of causing infant death
> in a homozygote, there should be some health benefit somehow to the
> heterozygote carriers.  In the case of Tay-Sachs, that benefit is an
> increased resistance to tuberculosis.  Another example is sickle-cell anemia
> gives the heterozygote carriers increased resistance to malaria.
> 
> Biology hipsters, what is that phenomenon called?  If I don't know the name
> of something I could waste hours Googleing around and finding nada.  Lee

There are several terms for it. 

https://en.wikipedia.org/wiki/Balancing_selection

I suspect it's more common than is generally recognized.

-rex
-- 
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