Question

If a colourblind woman marries a normal visioned man, their sons will be

• A. All normal visioned
• B. One-half colourblind and one-half normal
• C. Three-fourth colourblind and one-fourth normal
• D. All colourblind

Answer 1

The correct option is D All colourblind

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 colour blind (X${}^c$X${}^c$) and father is normal (XY). The affected mother will inherit the disease to all sons (X${}^c$Y). Correct answer is option D.
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 colour blind boy	X${}^c$Y colour blind boy