Probability of having a hemophilic baby

Hemophilia is an X-linked recessive genetic disorder, which means it is carried on the X chromosome. In this scenario, the mother is a carrier of the disease, which means she has one normal X chromosome and one X chromosome with the hemophilia gene. The father, on the other hand, is unaffected by the disease.

To determine the probability of having a hemophilic baby, we need to consider the inheritance pattern and the probability of passing on the hemophilia gene.

Inheritance Pattern
- Hemophilia is a sex-linked disorder, meaning it is more common in males. This is because males have only one X chromosome, while females have two X chromosomes.
- If a male inherits the hemophilia gene, he will have hemophilia because he does not have a second X chromosome to counteract the effects of the gene.
- Females, on the other hand, need to inherit the hemophilia gene from both parents to have the disorder. If they inherit the gene from only one parent, they will be carriers like the mother in this scenario.

Probability Calculation
- Since the father is unaffected by the disease, we can assume he has two normal X chromosomes (XN).
- The mother is a carrier, which means she has one normal X chromosome (XN) and one X chromosome with the hemophilia gene (Xh).
- There are four possible combinations of the X chromosomes that the parents can pass on to their child: XN from the father and XN from the mother, XN from the father and Xh from the mother, Xh from the father and XN from the mother, and Xh from both parents.
- The probability of passing on each of these combinations is 0.5 or 50%, as there is an equal chance of passing on either X chromosome.
- Out of the four possible combinations, only one results in a hemophilic baby (Xh from both parents).
- Therefore, the probability of having a hemophilic baby is 1 out of 4, which is equal to 0.25 or 25%.

Conclusion
The probability of having a hemophilic baby if the mother is a carrier and the father is unaffected is 0.25 or 25%. This means that in a large number of offspring, approximately 25% will have hemophilia while the remaining 75% will either be unaffected or carriers themselves.