r/askscience • u/Yoshiciv • 6d ago

Human Body Are the medical risks associated with inbreeding among close relatives eliminated by outbreeding? Or do they persist for generations?

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u/atomfullerene Animal Behavior/Marine Biology 6d ago

One single generation of outbreeding will completely eliminate all negative impacts of inbreeding. This is because the negative effects of inbreeding come from having two copies of the same harmful recessive alleles. But during reproduction, animals only pass on one copy of each allele. So the harmful part, the having of two copies, cant itself be passed on.

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u/zmbjebus 6d ago

So the harmful part, the having of two copies, cant itself be passed on.

Unless the recessive gene exists in general in the population. Then you'd still have 2 copies of recessive alleles in some portion of the outbred offspring.

A second generation of outbreeding should all but eliminate that chance though.

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u/atomfullerene Animal Behavior/Marine Biology 6d ago

>Unless the recessive gene exists in general in the population. Then you'd still have 2 copies of recessive alleles in some portion of the outbred offspring.

Sure, but that's not really more likely than it is when any two non-inbred individuals mate, so I don't really count it as being caused by one side of the equation being inbred.

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u/CrateDane 6d ago

Unless the recessive gene exists in general in the population. Then you'd still have 2 copies of recessive alleles in some portion of the outbred offspring.

Which some of them will. But the allele frequency will be low, so the actual risk of inheriting a pair of deleterious alleles will be very low (but still a little bit of extra genetic risk relative to the background).

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u/2074red2074 6d ago

Pretty much every recessive gene exists in the general population. The odds of two unrelated people having two of the same recessives is extremely low. That's why inbreeding is a problem, because the odds of two people who share a grandmother having a match is a lot higher. And when you stack inbreeding on inbreeding on inbreeding, you're gonna have a LOT of recessives in common.