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Captain-Griffen t1_jdotex7 wrote

Reply to comment by Mr_Mojo_Risin_83 in ELI5: How come recessive genes don't die out? by JackytheWriter

Recessive genes are, in fact, tougher for natural selection to completely eliminate than dominant ones.

If you have only 1% having the gene, only 1% of carriers will express the gene and be selected against. Meanwhile, any predators exploiting that gene would be getting almost no benefit, pushing them away from that behaviour.

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Mr_Mojo_Risin_83 t1_jdoucxb wrote

in the case of the goldfish though, if only 1% carry the gene, then there's almost no bright gold ones and when there are, the birds can see them and eat them easier. the bird is unlikely to push away from the behaviour of 'being able to see brightly coloured things more than dark things.'

if the other 99% aren't carrying the gene at all then they carry on reproducing dark colours with absolutely no chance of their offspring being gold coloured.

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Imaginary_Wolf_8698 t1_jdq6gxp wrote

That’s not a recessive gene though. If 1% of the population carries a recessive gene (and assuming it’s equally in male and female) then 0.025% of the population or 1 in 40000 offspring will actually have the recessive trait. This is why it’s almost impossible to eliminate a recessive gene from a gene pool.

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Mr_Mojo_Risin_83 t1_jdq6yeh wrote

yeah i was using the figures supplied by the person above. in most real situations, we usually have a broader dispersion of genetics than 99% vs 1%.

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Mr_Mojo_Risin_83 t1_jdowvga wrote

also, any gene that's only carried by 1% of a population will almost surely disappear anyways. even if it's not detrimental to survival. if you have a pond of 100 fish and only 1% carry the gene, then a bird comes and eats 20 x fish, there's a random chance the 1 fish with the gene will be removed from the gene pool entirely. whereas the other 99% will always have numbers among the survivors.

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ZacQuicksilver t1_jdpo7qd wrote

That's true if there is 100 fish - but not if there is 1 000 000 fish.

If there's a huge number of fish, the chance that a given gene is removed randomly is very low. Unless it provides a disadvantage, it's entirely random. There have been experiments, both in digital environments and in sealed live environments, tracking genetic drift (the change in gene representation in a population over time); and pretty consistently there are cases of genetic variations that end up spreading by chance that don't do anything.

The classic example of real-life variations are two different genes that code for the same amino acid chain using different base pairs - there's no advantage one way or another. In such a case, the most common result over time is that both versions of the gene persist; even if you start with one variation is less common than the other.

The exception is if you simulate bottlenecks - like the "100 fish" scenario you posted. With such small numbers getting through, it becomes a lot more likely for some genes to be lost forever by random chance - including useful genes that happen to get unlucky.

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