Post 2: How does one inherit hemophilia?

Hemophilia is an x-linked disease. Although both genders can acquire the disorder, it is more common for males to show the symptoms. This is because of the chromosomal make-up of humans. Males are XY, females are XX. Hemophilia afflicts the X chromosome, so if a male has an affected X chromosome, he has the disease. Females, however, are different. Because they have two X chromosomes, it’s very rare for a woman to get the disorder. This is because their “good” X overshadows their bad one (since hemophilia is recessive). In the event that both of her Xs are affected, she has hemophilia and will display the same symptoms (profuse bleeding, easy bruising, etc.) that any male with the disease would. In fact, there are only two ways for a female to have hemophilia; if the father and the mother both have the disease. The other way is if the father is affected but the mother is a carrier. Here are two Punnett Squares to display what I mean. Punnett Square 1 symbolizes the first possibility (both parents have the disease) and Punnett Square 2 symbolizes the second possibility that which a female can get hemophilia.

A female can be a carrier as well, meaning only one X is affected; she wouldn’t exhibit the symptoms that a man would show, but she can spread the disease to her offspring, even with a husband who tests negative for the disease. Likewise, a positive man can cause his daughters to be carriers. These facts can be evidenced by the following Punnett Squares:

As seen in Square 3, the carrier mother takes a seventy-five percent chance of giving the disease to her kids; one hundred percent chance of making a daughter a carrier and fifty percent chance of causing her son to be a hemophiliac. To continue, a hemophilic father mating with an unaffected woman would certainly cause one hundred percent of daughters to be carriers. No sons would be affected as proven by Square 4.

Hemophilia is a recessive x-linked disease that mostly affects men, but in rare cases, can afflict women as well.