Short Answer 
Hemophilia is a genetic disorder linked to the X chromosome that can affect blood clotting, primarily impacting boys who inherit the affected X. Sons of Kate Middleton and Prince William have a 50% chance of having hemophilia, while daughters have a 50% chance of being carriers but are unlikely to exhibit the disorder due to inheriting a healthy X from their father.
Step 1: Understand Hemophilia and Inheritance
Hemophilia is a genetic disorder that primarily affects the blood’s ability to clot, linked to the X chromosome. Since it is a recessive disorder, the gene’s presence on one X chromosome can manifest in boys but not necessarily in girls. This genetic mechanism is crucial in determining how the disorder can pass from parent to child.
Step 2: Evaluate the Risk for Sons
Each son of Kate Middleton and Prince William has a 50% chance of inheriting hemophilia. This is because they receive their Y chromosome from their father and an X chromosome from their mother. If a son inherits the X chromosome carrying the hemophilia gene from Kate, he will exhibit the disorder since there is no corresponding gene on the Y chromosome to counter it.
- Sons inherit XY chromosomes: X from the mother, Y from the father.
- If the son gets the affected X from Kate, he will have hemophilia.
- Each son has a 50% chance of having the disorder.
Step 3: Assess the Risk for Daughters
Daughters of Kate and William have a 50% chance of being carriers of hemophilia. They inherit one X chromosome from each parent, which means even if they get the affected X from Kate, the healthy X from William will usually prevent them from having the disorder. However, this makes them carriers, similar to their mother.
- Daughters inherit XX chromosomes: one X from both parents.
- Even with the affected X, a healthy X from William prevents the disease.
- Each daughter has a 50% chance of being a carrier but is unlikely to have hemophilia.