If a Hemophilia carrier gives birth to two sons, what is the probability that both boys will have the disease?

What approach to probability are you using to answer this question?

Hemophilia A occurs in 1 in 10,000 people. Hemophilia B occurs in 1 in 40,000
http://www.emedicinehealth.com/hemophili...


If the mother carries the gene for hemophilia on one of her X chromosomes, each of her sons will have a 50% chance of having hemophilia.
http://www.kidshealth.org/teen/diseases_...

depends if the father was a carrier as well and if the disease was dominate or recessive.

if that father is also a carrier then you have a higher chance. it also depends if the gene is dominate or recessive. lots of things are considered when you're looking a problem this serious.

Everyone inherits two sex chromosomes, X and Y, from his or her parents. A female inherits one X chromosome from her mother and one X chromosome from her father (XX). A male inherits one X chromosome from his mother and one Y chromosome from his father (XY). The gene that causes hemophilia is located on the X chromosome.

A woman who gives birth to a child with hemophilia often has other male relatives who also have hemophilia. Sometimes, a baby will be born with hemophilia when there is no known family history. This means either that the gene has been "hidden" (that is, passed down through several generations of female carriers without affecting any male members of the family) or the change in the X chromosome is new (a "spontaneous mutation").

There are four possible outcomes for the baby of a woman who is a carrier. These four possibilities are repeated for each and every pregnancy:
1. A girl who is not a carrier
2. A girl who is a carrier
3. A boy without hemophilia
4. A boy with hemophilia

With each pregnancy, a woman who is a carrier has a 25% chance of having a son with hemophilia. Since the father's X chromosome determines the baby will be a girl, all the daughters of a man with hemophilia will be carriers. None of his sons, which is determined by the father through his Y chromosome, will have hemophilia.

You have two independent events; so the probability of both occurring together is the product of the individual probabilities.

In other words, the probability that both boys are haemophiliacs is the square of the probability that one boy will be a haemophiliac.

If a hemophiliac carrier gives birth to two boys, there is a 1 in 4 chance than they both with have hemophilia (1 in 2 for each boy, so 1/2 x 1/2 = 1/4 that both will get it).