Which one of the following disorders is a sex linked recessive disease?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Haemophilia
Option (1) Sickle-cell anaemia — Incorrect. It is autosome-linked recessive. One base change in the β-globin gene puts valine in place of glutamic acid, and the red blood cells become sickle-shaped at low oxygen.
Option (2) Haemophilia — Correct. The gene is on the X chromosome. A protein of the blood-clotting chain is missing, so a small cut keeps bleeding. It passes from carrier mothers to some of their sons; a haemophilic female is very rare.
Option (3) Phenylketonuria — Incorrect. It is an autosomal recessive error of metabolism: the enzyme that converts phenylalanine is missing, and the build-up harms the brain.
Option (4) Thalassemia — Incorrect. It is also autosome-linked recessive. Too few globin chains are made, giving anaemia.
NCERT Extract:
Mendelian Disorders – “… Haemophilia : This sex linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progeny has been widely studied. In this disease, a single protein that is a part of the cascade of proteins involved in the clotting of blood is affected. Due to this, in an affected individual a simple cut will result in non-stop bleeding.”