Question

In the progeny of a color blind woman and a normal man _____________

• A. All the sons are normal
• B. All the sons are colour blind
• C. All the sons and all the daughters are color blind
• D. All the daughters are color blind

Answer 1

Answer: (B)

The correct option is B All the sons are colour blind

• Colour blindness is an X-linked recessive disorder. Since daughters receive one copy of X-chromosome from the father, a normal man cannot have colourblind daughters.
• This is due to the fact that females with two copies of the affected gene show the disorder (X${}^c$X${}^c$ ) while females heterozygous for this trait will be normal but serve as a carrier of the disease.

The colourblind mother (X${}^c$X${}^c$ ) would transmit the affected X chromosome to all of her daughters which will then serve as carriers. Son receives its X chromosome from mother which is colour blind here (X${}^c$$X^c$) which means mother would transmit affected copy of X-chromosome to all of her sons (X${}^c$Y) making them colour blind. Thus, the correct answer is option B.