Haemophilia is inherited through a gene that is:

1. Haemophilia is a failure of the blood to clot normally. 2. The gene responsible is recessive, so it is masked whenever a normal allele is present. 3. It is carried on the X chromosome, making it sex-linked. 4. A male has only one X, so a single recessive allele shows in him; a female needs two to be affected. 5. That is why the condition appears far more often in males, and why writing the alleles without linking them to the X chromosome loses the whole pattern. _Source: NECTA ACSEE 2023 Biology 133/2, Question 4: Genetics_