Hemophilia is a sex-linked recessive disorder.  A man with hemophilia mates with a woman who is a carrier for the disease.  What percentage of their children will get hemophilia ?

Hemophilia is a sex-linked recessive disorder. This means that it is carried on the X chromosome. Males have one X and one Y chromosome (XY), and females have two X chromosomes (XX).

The man with hemophilia has the disorder, which means his X chromosome carries the hemophilia gene (we'll denote this as Xh). His Y chromosome doesn't carry the gene (denoted as Y). So, his genetic representation is XhY.

The woman is a carrier for the disease, which means one of her X chromosomes carries the hemophilia gene and the other doesn't. We'll denote this as XhX.

When they have children, each parent contributes one chromosome to the child.

1. If they have a son (XY), the son gets the Y chromosome from the father (since only males have the Y chromosome). The son has a 50% chance of getting the X chromosome with the hemophilia gene from the mother. So, there's a 50% chance the son will have hemophilia.

2. If they have a daughter (XX), the daughter gets the father's X chromosome (which carries the hemophilia gene) and has a 50% chance of getting the mother's X chromosome with the hemophilia gene. This means there's a 50% chance the daughter will be a carrier like her mother (XhX), and a 50% chance she'll have hemophilia (XhXh).

So, overall, each child has a 50% chance of having hemophilia, regardless of their sex.