Question

An X-linked recessive trait is?

• A. Colour blindness
• B. Hunter's syndrome
• C. Sickle-cell anaemia
• D. Leishman's syndrome

Answer 1

The correct option is A Colour blindness

Traits that are determined by alleles carried on the X chromosome are referred to as X-linked. X-linked alleles require a specific notation: Xc or X+ where the “+” represents the dominant allele and the lowercase letter the recessive allele. Females will have two X-linked alleles (because females are XX), whereas males will only have one X-linked allele (because males are XY). Most X-linked traits in humans are recessive. One example of an X-linked trait is red-green colorblindness. Let (Xc) represent the recessive allele that causes colorblindness and (X+) represent the normal dominant allele. Females that are X+X+ or X+Xc have normal color vision, while XcXc females are colorblind. Males that are X+Y have normal color vision, while XcY males are colorblind.

So, the correct answer is 'Colour blindness'.