Why does inbreeding result in a higher chance of genetic defects?
In: Biology
Genetic birth defects are usually recessive traits, meaning it requires two copies of a gene to activate.
If your father carries the genes for Tay-Sachs (a genetic illness responsible for killing children painfully), but your mother doesn’t, then both you and your sister are going to be healthy.
But you each have a 50% chance of carrying the gene. Let’s say you both do. If you two have incest-babies, you will have a 50% chance of your child being a carrier & a 25% chance of your child being a Tay-Sachs baby.
But if you marry outside the family, the chances of getting together with another Tay-Sachs carrier are small, and thus your child is less likely to have the condition.
It’s not just known genetic conditions, it’s also random junk changes in the DNA caused by replication that don’t cause any problems when they aren’t duplicated in the DNA.
And as for less damaging genetic traits, like imperfections in the eyes or nose, or extra fingers or other weirdness, the inbreeding essentially selects for those traits as “desirable” and makes them more prominent.
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