Question

If a colourblind man is married to a normal woman, then from the point of view of disease, their offsprings will be

• A. All sons will be colourblind.
• B. All daughters will be colourblind.
• C. All sons and daughters will be normal.
• D. All sons and daughters will be colour blind.

Answer 1

The correct option is C All sons and daughters will be normal.

Colour blindness is a X-linked recessive disorder. One copy of the affected gene in males in each cell is sufficient to cause the disorder (X${}^c$Y). Females with two copies of the affected gene show the disorder (X${}^c$X${}^c$). Females heterozygous (X${}^c$X) for this trait be normal but serve as a carrier of the disease. According to the question, the female is normal (XX) and father is colour blind (X${}^c$Y). The affected father will inherit the affected allele (X${}^c$Y) to all daughters who will have normal vision but serve as carrier. Correct answer is option C.
Parent generation : XX x X${}^c$Y

Gametes : XX ----> X${}^c$Y	X	X
X${}^c$	X${}^c$X carrier girl	X${}^c$X carrier girl
Y	XY normal boy	XY normal boy