Can a brother have kids with his sister?

Many cultures encourage first cousin marriages and their kids seem to be pretty safe. Recent studies have shown that the risk for first cousins to pass on diseases is only 2-3% higher than for unrelated people. But there is definitely good biology behind the laws that prohibit brothers and sisters from having children.

What happens if a mother cat mates with her son?

Bella: Mother cats and their kittens can and do mate. It certainly increases the risk for birth defects and other problems because kittens created through a mother-child mating can get double copies of bad genes. But plenty of vets have spayed pregnant cats with no problems.