In the United States, I believe it is mandatory for both parties to have
a blood test prior to being married. I'm supposing this would 'guide'
the couple in their decision to have a family, should any genetic
clashes show up. On my father's side, his mother passed on the
gene for Muscular Dystrophy. I've been told that this gene is passed
down the female line, and can effect males. My grandmother was married
twice, the first marriage bore 2 sons, the second 2 daughters. One of the
daughter's had a boy, born with Muscular Dystrophy, he lived into his teens.
The other daughter had a girl, who had no problems but concerns arose
when she herself was pregnant with a boy. In this instance he was okay.