Question

If a colourblind woman marries with a normal man. The offspring will be

• A. All colourblind
• B. AIl daughters will be normal and all sons will be colourblind
• C. All normal
• D. All daughters will be colourblind and all sons will be normal

Answer 1

The correct option is B AIl daughters will be normal and all sons will be colourblind

Colourblindness 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 are normal but serve as a carrier of the disease. According to the question, the female is colourblind (X${}^c$X${}^c$) and father is normal (XY). The affected mother will inherit the disease to 100% sons (X${}^c$Y) while the 100% daughter will be normal but will serve as carrier. Correct answer is option B.
Parent generation: (X${}^c$X${}^c$) x XY

Gametes : (X${}^c$X${}^c$) --> XY	X${}^c$	X${}^c$
X	X${}^c$X carrier girl	X${}^c$X carrier girl
Y	X${}^c$Y colourblind boy	X${}^c$Y colourblind boy