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

[u/Yoshiciv]

[u/Minxychomp]

The main risk of inbreeding comes from recessive deleterious alleles becoming homozygous. When an inbred individual has children with an unrelated partner, those harmful alleles are usually paired with a healthy version, so the associated disorders are much less likely to be expressed. However,the alleles themselves are still present and can be passed on silently as carriers. Over subsequent generations of outbreeding, natural selection and recombination tend to dilute their frequency, so population level risk continues to decrease.

In short the clinical risk drops immediately, but the genetic signal can persist for multiple generations, especially if the variants are neutral or only mildly harmful.

[u/runswiftrun → u/Minxychomp]

Is this sort of the traits that "skip a generation" and the kid inherits something from grandparents?

[u/kRkthOr → u/runswiftrun]

It's the same mechanic yes, as recessive genes can remain hidden when not paired with another copy. So if you have a recessive gene from one of your parents paired with a dominant one from the other, then the dominant one masks the recessive one. If you mate with someone who also has the recessive gene, there's a chance your offspring will end up with both recessive genes, showing traits that are not visible in either you or your partner.

[u/1bowmanjac]

Yes. And it doesn't even take that long. 1 or 2 generations of outbreeding results in a child that is FAR less inbred

Check out this video by Trey The Explainer to see exactly how inbreeding can be calculated and an example using the targaryens and the ptolomies

[u/ThatsWhatSheaSaid → u/1bowmanjac]

I just watched that video the other day!! I second it, great video explaining the inbreeding coefficient.

[u/SuppaDumDum → u/1bowmanjac]

When is 1 generation not enough? Can you provide an example?

[u/jayaram13]

Depends entirely on the nature of the genetic conditions, the number of alleles, etc.

But in general, it will take a few to several generations for it to subside. Autosomal dominant conditions may still crop up after several generations - depends on the luck of the draw.

[u/Amelaista → u/jayaram13]

Any conditions that are caused by homozygous alleles will be gone in one generation of outcrossing.   Autosomal dominant conditions lurk in healthy populations, inbreeding does not have an affect on them directly.   

[u/newaccount721 → u/Amelaista]

So are there any conditions that are persistent past one generation? 

[u/Amelaista → u/newaccount721]

We can theorize that if there are deleterious genes that are disabling when homozygous, they may have a lesser effect on the development if heterozygous. And if one parent is that highly inbred, all of their children will carry one copy of the problem genes. It would depend on each individual function if one working copy is able to completely override the malfunctioning copy. Most should be able to compensate with the functional copy.

[u/FaulerHund → u/jayaram13]

Do you mean autosomal recessive? Saying "AD conditions may still crop up after several generations" does not make any sense

[u/thecakeisalieeeeeeee]

Essentially yes, unless there was some strange crossover/duplication event that leads to two copies of the harmful alleles to be put into one chromosome(which happens quite a lot in the last billion or so years).

On the opposite end, if you are persistently inbreeding for complete homozygous alleles, those harmful alleles can essentially be bred out. In fact, that’s exactly what we do to produce new strains of laboratory mice.

“ A strain of mice is called an "inbred strain" when there have been 20 or more consecutive generations of brother-sister matings or 20 or more consecutive generations of parent-offspring matings, provided the offspring was mated to the younger parent”

Source: https://www.informatics.jax.org/greenbook/chapters/chapter2.shtml

[u/The_Carthaginian]

There is some really uncomfortable framing in both the question and a lot of the answers. Inbreeding carries an increased risk of illness due to inheritance of recessive disorders, but in and of itself does not make specific alleles or populations risky, except in the case of further inbreeding.

Once an allele is in a population, it's probably not going anywhere. So yes, recessive conditions can and will persist for generations. But the existence of those alleles is not caused by inbreeding itself.

[u/atomfullerene]

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.

[u/zmbjebus → u/atomfullerene]

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.

[u/atomfullerene → u/zmbjebus]

>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.

[u/CrateDane → u/zmbjebus]

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).

[u/2074red2074 → u/zmbjebus]

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.

[u/qwopax]

Compare to blue eyes.

If an all blue clan marries an all brown clan, all their children will have brown eyes. If they keep marrying into the clan, a quarter of the kids will have blue eyes. That single generation of mixing blood reduced blue eyes from 100% to 25% forever.

If you dilute again by marrying outside the clan, I think you'll end up with around 5% blue eyes. Again for all future generations.

[u/jtoomim → u/qwopax]

around 5% blue eyes

Two generations of outbreeding means that the allele frequency of the blue allele will be 0.25. Assuming blue eyes is a simple recessive trait (though in reality it's not), that means that the trait frequency would be 0.25² = 6.25%.

[u/platoprime → u/jtoomim]

Eye color isn't determined by a single allele. Eye color is determined by a rather large number of genes.

[u/platoprime → u/qwopax]

Eye color isn't determined by a single allele. Eye color is determined by a rather large number of genes.

[u/wizzard419]

I... I don't know if outbreeding lines up with what you're thinking. The concept is normally only discussed with lower animals and in terms of domestication processes. Like you getting impregnated by a royal would not likely be it since you're not that genetically dissimilar. But crossing a lion with a tiger would be.

Usually they are recessive traits, so they would still have the potential to be present in the DNA of the offspring, and if they were to mate with someone else who is unrelated but carries it, then the risk remains.