@Hello03 actually ur kinda right and wrong inbreeding with ur cousin is not the exact same as with siblings. and I agree with
@amanimal it has to be done with every generation for a flaw to happen cause every time it doesn't new blood gets in the mix witch reduces the possibility of it happening my uncle and aunt marries their cousin and their children turned out completely fine one had 2 children the other had 5 again with no issues at all its not as high of a possibility between cousins as u may think
According the Clinical Genetics Handbook, children of non-related couples have a 2-3% chance of being born with a birth defect, and children of first cousins have a 4-6% chance