Short Answer 
Hemophilia is a genetic disorder linked to the X chromosome, affecting males and females differently. Sons of Kate and William have a 50% chance of having hemophilia, while daughters have a 50% chance of being carriers without likely showing symptoms.
Step 1: Understanding Hemophilia
Hemophilia is a genetic disorder caused by a deficiency in certain clotting factors in the blood, making it hard for individuals to stop bleeding. It is linked to the X chromosome, which means that males and females are affected differently by this condition. This distinction is crucial in understanding the inheritance patterns for the children of Kate Middleton and Prince William.
Step 2: Probability for Male Offspring
Each son of Kate and William has a 50 percent chance of having hemophilia. Since sons inherit one X chromosome from their mother and a Y chromosome from their father, if a son gets the X chromosome that carries the hemophilia gene from Kate, he will have the disorder. This is because a Y chromosome from their father does not possess a corresponding gene to counteract the affected X chromosome.
- They receive X from mother (Kate) and Y from father (William).
- Probability of inheriting affected X: 50%.
- If they inherit affected X, they will have hemophilia.
Step 3: Probability for Female Offspring
Daughters of Kate and William have a 50 percent chance of being carriers of the hemophilia gene, but it is unlikely they will have the disorder. Females inherit one X chromosome from each parent, so even if they receive the affected X chromosome from their mother, the healthy X from their father will prevent them from manifesting the disease. Therefore, they may carry the gene without showing symptoms.
- They receive X from both parents (X from Kate; X from William).
- Probability of being a carrier: 50%.
- If they have one affected and one healthy X chromosome, they become carriers.