Posted: Dec 04, 2022 8:40 am
Symbiont wrote:If all humans are genetically similar; why is inbreeding bad?
Genes with very harmful traits aren't expressed when they are recessive, only when there's 2 copies of them.
In some populations, these traits can survive perfectly well while recessive as they either don't harm the individual, or maybe even offer some other benefit.
So if a particular nasty gene is fairly common in a population, and if individuals in that population continually breed among themselves, the chances of these harmful traits being expressed increases.
Symbiont wrote:
Since we're 99.9% genetically similar as is assumed. Then inbreeding shouldn't be an issue but it obviously is and since inbreeding is an issue. Then we humans aren't 99.9% genetically similar.
Am I missing something?
Aside from the point above, this isn't very clear reasoning.
It's equivalent to saying that 99.5% of the time you drive your car, you don't have an accident, and concluding that therefore vehicle accidents can't occur. It's not the 99.5% that's the problem, it's the 0.5% you have to account for.
There are 3 billion base pairs of DNA in the human genome.
99% of 3 billion is 2,985,000,000 that still leaves 15,000,000 which differ. On the occasion when some of those remainder happen to include a dominant and recessive copy of a deeply harmful trait, then bad results occur.