[removed]

Without going into too much detail, the odds of something bad go down exponentially, specifically with 1/2 for every extra link in the family tree away from a shared ancestor. 1/8, 1/16, and 1/32 odds per gene (3,4, & 5 links, respectively) are pretty bad across >20,000 genes, but it doesn't take a lot of distance (14 links) before your risk drops to 1/16384, at which point it's basically trivial. By the time you're 3rd or 4th cousins, you're basically genetically unrelated.

[removed]

It depends on luck and how closely related they are to you and how inbred the population is. The more times it happens the more likely the problems. If you’re thinking ahead for purposes of reproduction, see an expert with as much information about her family and yours before you make a commitment.

Assuming no history of inbreeding and little/no chance your future kids will inbreed, 1st cousin is generally safe as a one off. It raises the genetic risks a bit but not enough to be a red flag. Obviously there are present day social mores to be concerned about.

The further you go from that the better, about 5 steps is probably sufficient though (closest shared ancestor is your great-great-great-great grandparent).

But really the problem with inbreeding is repeated incidents, as you are narrowing the gene pool significantly. This is a concern in more insular communities (like the Amish) where you don't get a lot of people from outside adding to the gene pool.

I’d add there’s an easy blood test to take called “genetic carrier screen” that’s relatively accessible. It will test each person for what genes they are carriers for. If both carry the same gene you know you have a 25% chance of passing on the active disease to a child

[removed]