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wpmason t1_j41kslj wrote

That is one reason genetic disorders can occur but far from the only reason.

Often times it’s just a one-off mutation that “breaks” a gene.

It can also just be a rare, recessive hereditary trait that would require both parents to be carriers of the affliction and still only give a 1 in 4 chance of the offspring having it.

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perta1234 t1_j42meit wrote

Yes and no. It is bit complicated. Some disorders are combinations of variants of different genes, so there it is not the cause. Some are caused by dominant gene variants, so there as well, relatedness does not play a role. But then there are the recessive disorders, where you must inherit similar bad variant from mother and father, so there relatedness does matter.

Close relatedness of parents increases the proportion of genes, where the child has two identical variants. If some proportion of the genes are coding recessive disorders, one is more likely have an disorder. It is the mutation or the genotype that causes the disorder. Relatedness has impact on the genotype. So relatedness can have an indirect impact, but that depends on the existence of those mutations or gene variants.

Most disorders are of the recessive type or something that was beneficial in a different environment.

We are all "somehow related".

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UnarmedSnail t1_j44t7s1 wrote

Genetic disorders can happen both from random mutation that happens just to one person, and inherited mutation passed down from the original mutated ancestor to descendents. An inheritable mutation must happen in an egg or sperm originally to be passed down, such as sicle cell anemia.

Random mutations otherwise, such as bone cancer in example, are not passed down. Random mutations appear the same a lot of the time because our genes can be broken in some ways more easily that others that cause rare diseases.

Our genome is a patchwork thing from several different human and human ancestor lines and it's amazing it all works together as well as it does.

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[deleted] t1_j42brth wrote

[removed]

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ScienceIsSexy420 t1_j42hpbb wrote

Mutations cause genetic disorders, but inbreeding increases the chances of inheriting those mutations. That's why you see things like the prevelance of Tay-Sachs in the Ashkenazi Jew population. Humans are especially vulnerable to inheriting genetic disorders due to inbreeding because of a lack of genetic diversity caused by previous population bottlenecks during prehistoric times.

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