Why do blood family members if they had a baby why is the baby risking genetic defects why does this happen? no real reason to ask i'm just curious.

Recessive genes: People in general possess some recessive genes. When unrelated people have a child, it is far less likely to have both possessing the same recessive genes. With minor exceptions, genetic diseases do not show up unless the baby inherits both recessive genes. Since related people are more likely to possess the recessive genes, the risk of genetic defect rises significantly when they are related