Which one of the following genetic diseases is sex-linked?

1. The question asks to identify the sex-linked genetic disease among the options. 2. Sex-linked diseases are genetic disorders caused by mutations in genes located on the sex chromosomes (X or Y). Most are X-linked. 3. Royal haemophilia (Haemophilia A or B) is a classic example of an X-linked recessive disorder, affecting blood clotting. It is called 'Royal' because it affected several European royal families. 4. Tay-Sachs disease is an autosomal recessive genetic disorder. 5. Cystic fibrosis is an autosomal recessive genetic disorder. 6. Hypertension (high blood pressure) can have genetic components, but it is a complex, multifactorial condition, not a simple sex-linked genetic disease. 7. Therefore, Royal haemophilia is the sex-linked disease.