Ok...seems that when you guys talk about genes you didn't check posts I and
Vegeta made earlyer in this thread, but anyway...
There is possibility that children get genetic disease when relationship is between
cousins, but possibility for that is only few % and alot of people are ready
to take that change. With inside family, bothers/sisters and so on, change
of getting healthy baby is much smaller, close to 50/50 change.
So stop speacking about genes if you just don't know anything.
And please, like Vegeta said earlyer little tolerance to your post.
They actually might hit someone quite hard.