# Evolution: why are mutations retained by descendants?

**URL:** <https://boards.straightdope.com/t/evolution-why-are-mutations-retained-by-descendants/605768>\
**Category:** Factual Questions\
**Created:** [December 10, 2011, 9:42pm UTC](https://boards.straightdope.com/t/evolution-why-are-mutations-retained-by-descendants/605768 "2011-12-10T21:42:32Z")\
**Posts on this page:** 1\
**Page:** 2

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**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\
**Post date:** [December 11, 2011, 9:01pm UTC](https://boards.straightdope.com/t/evolution-why-are-mutations-retained-by-descendants/605768/21 "2011-12-11T21:01:22Z")

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> [@](#):
>
> Quoth **septimus** :  
> In other words, you expect 1/16 of one’s g-g-grandchildren to inherit the full gene, rather than each g-g-grandchildren to inherit 1/16 of the gene.

Much more succinct than how I put it, thank you.

And to add to **md2000** ’s bit about how selective pressure gets weaker on rare recessive genes, it should also be noted that once the bad gene gets rare, it might disappear anyway, just by random chance. Or, of course, it might make a comeback, if a few particularly successful individuals happen to have one copy of it.

The existence of such rare recessive defects is also, incidentally, the reason why inbreeding is a bad idea. Everyone has a handful of these rare recessive defect genes, but they’re almost never relevant, since the chance of mating with someone else who happens to share one of those same defective genes is so low. But siblings or other close relatives have a pretty good chance of sharing at least a couple of them, in which case their offspring would be likely to express them.

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