Under what circumstances it is possible for a father and a son to suffer from haemophilia?

Explanation

### Step-by-Step Solution:

1. **Understanding Hemophilia**: Hemophilia is a genetic disorder that impairs the body's ability to make blood clots, a process that is essential for stopping bleeding. It is primarily an X-linked recessive condition.

**Hint**: Remember that hemophilia is linked to the X chromosome, which is crucial for understanding inheritance patterns.

2. **Genetic Makeup**: In humans, males have one X and one Y chromosome (XY), while females have two X chromosomes (XX). For a male to be affected by hemophilia, he must inherit the X chromosome carrying the hemophilia allele.

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