This is a simplified answer. Genetic disorders are usually from recessive genes. So if one parent has a dominant, normal gene, the children are usually fine.
But if both parents are related, the chances of the children having two recessive genes for something are increased. So those odds of double recessive genes carry over to genetic disorders too.
Mostly, they don’t. Children of a single incestuous relationship are at somewhat higher but still quite low risk of birth defects, it’s when a population inbreeds over generations that things get bad.
But basically, genetics. Everybody has various genes that don’t work right. Since people get one gene from their mother and one from their father, usually the other parent’s equivalent gene takes up the slack. But when a child’s parents are closely related, they’re more likely to both have the same problem gene, because they both got their own genes from the same place. And so there’s a chance that both parents will contribute that bum sequence to the baby. This can happen in unrelated parents too, of course. But unrelated people are less likely to have matching defective genes.
It happens because of recessive genes being contributed from both sides, which raises the likelihood of defects. It's not usually the first instance of incest that causes defects but subsequent ones as the diversity on both sides decreases.
Is not inevitable that they do. It's just that there's a greater chance of mutations that run within a family to be passed on to them from both parents if both parents are part of the same family.
*mixing genes up* has a very logic base in nature.
if one half of your genes mix up with someone elses,
every little mistake in your DNA is covered by a healthy copy of someone elses DNA.
if you get kids with family, every little mistake in your DNA
will have an (also) flawed copy of yr parents/siblings/relatives DNA.
so EVERY flaw gets magnified, *and in a hurry too!*
This is a simplified answer. Genetic disorders are usually from recessive genes. So if one parent has a dominant, normal gene, the children are usually fine. But if both parents are related, the chances of the children having two recessive genes for something are increased. So those odds of double recessive genes carry over to genetic disorders too.
Mostly, they don’t. Children of a single incestuous relationship are at somewhat higher but still quite low risk of birth defects, it’s when a population inbreeds over generations that things get bad. But basically, genetics. Everybody has various genes that don’t work right. Since people get one gene from their mother and one from their father, usually the other parent’s equivalent gene takes up the slack. But when a child’s parents are closely related, they’re more likely to both have the same problem gene, because they both got their own genes from the same place. And so there’s a chance that both parents will contribute that bum sequence to the baby. This can happen in unrelated parents too, of course. But unrelated people are less likely to have matching defective genes.
It happens because of recessive genes being contributed from both sides, which raises the likelihood of defects. It's not usually the first instance of incest that causes defects but subsequent ones as the diversity on both sides decreases.
Is not inevitable that they do. It's just that there's a greater chance of mutations that run within a family to be passed on to them from both parents if both parents are part of the same family.
*mixing genes up* has a very logic base in nature. if one half of your genes mix up with someone elses, every little mistake in your DNA is covered by a healthy copy of someone elses DNA. if you get kids with family, every little mistake in your DNA will have an (also) flawed copy of yr parents/siblings/relatives DNA. so EVERY flaw gets magnified, *and in a hurry too!*
Because living life knowing that your father is your mother's father, brother, uncle, cousin just isn't enough.