Haemophilia is an X linked disease. Ie its on your X chromosome. Women have 2Xs, men have XY. If a man gives a child his X, they have a daughter (mums always give Xs), if a Y, the child is XY (son).

Men are XY, so if they have a daughter, the daughter will definitely get a faulty X from dad. Theres one X, and its faulty wrt haemophilia. But most likely a healthy X from Mom. 1 healthy X is sufficient to be very normal. 2 bad Xs normally don't happen - pregnancy often doesn't reach term

My Mum's father had it , of his 4 kids, the 3 girls are all guaranteed to be carriers (1 good X 1 bad).

The brother of my grandpa is a man, got the Y from grandpa..i.e a haemophiliac male has no chance of giving it to his son. But all the daughter's are carriers.

So haemophilia ended for most of my wider family - my uncle and his kids can't have it, one auntie never married, 1 auntie was a carrier but had 1 daughter (almost 0% chance, but 50% of being a carrier...but she ended up not even being that), and 1 son (flip a coin on getting the good or bad X).

In my case, my mum had 2 sons...50% chance for each of us having it. We both do.

It's really not that pervasive as it skips a generation every time.

None of any kids i have, will have haemophilia. If i have only sons, Haemophilia ends for any of my future generations. If i have daughters, each will certainly be a carrier, but only have a 50% chance of making their own children a carrier (girl) or a haemophiliac (boy).