Which of the following is a hereditary disease ?

Question

Accepted Answer

The correct option is (2):
Colour blindness, particularly the most prevalent red-green colour deficiency, is classified as a hereditary disease because it is directly caused by a faulty gene passed from a parent to their child. This genetic condition is typically an X-linked recessive trait, meaning the gene responsible is located on the X chromosome. As males possess only one X chromosome (XY), they are affected if they inherit the faulty gene, making them much more vulnerable. Females, with two X chromosomes (XX), are often asymptomatic carriers, as the second, healthy X chromosome typically compensates for the flaw. Since the disorder is inherent in the individual's genetic code at birth and cannot be contracted through external exposure, it perfectly aligns with the definition of a hereditary disease.

The incorrect option is (1):
Rabies is fundamentally a viral, infectious disease, not a hereditary one. It is caused by the Lyssavirus genus and is acquired through contact, primarily via the bite or scratch of an infected animal, such as a dog, bat, or wild mammal. The virus travels to the central nervous system, leading to fatal encephalomyelitis. Its transmission is purely dependent on exposure to the pathogen, and there is no evidence of a genetic or inherited component that causes the disease itself. Therefore, it is categorized as an acquired communicable disease.

The incorrect option is (3):
Polio, or poliomyelitis, is an infectious disease caused by the poliovirus. Transmission occurs person-to-person, typically through the fecal-oral route, often via contaminated water or food. It is a highly contagious disease that attacks the nervous system, potentially leading to paralysis. Although an individual's immune system response may be genetically influenced, the *cause* of the disease is the external poliovirus. It is prevented by vaccination and is not a condition passed down through generations of genetic inheritance, making it an acquired, non-hereditary infection.

The incorrect option is (4):
Smallpox was an acute, highly contagious infectious disease caused by the Variola virus. Its clinical presentation was characterized by a severe rash and high fever, and it spread through direct and prolonged contact between people. It is a landmark disease in global health, as it was successfully eradicated through a worldwide vaccination campaign. Like Rabies and Polio, Smallpox was caused by a specific, external pathogen and was acquired via transmission, not through the inheritance of a genetic mutation from one's parents.