Rohan, a colour blind man is married to Aashima, a carrier woman with normal vision. Colour blindness is a genetic disorder in which people are not able to distinguish between red and green colours. Rohan and Aashima are scared about the possibilities of the transmission of this disorder in their children.

(i) The defective gene of colour blindness is located on the X-chromosome which can be found in both- male and female sex chromosomes. Which of the following statements is/are incorrect ?

1. Colour blindness is a recessive sex-linked disorder.
2. It is caused by a dominant allele, located on all sex chromosomes, when a person is colourblind.
3. It is more common in females.
4. Both (2) and (3)

(ii) Aashima delivered a baby girl via her first pregnancy. Which of the following features are not possible in her daughter ?

1. The daughter may be colourblind.
2. The daughter may be carrier with normal vision.
3. The daughter has a normal vision without the defective gene on the chromosomes.
4. Both (1) and (2)

(iii) After three years, Aashima conceived and delivered a baby boy. The couple was very happy because they heard that the disorder is X-linked and would not pass down to their son. Choose the correct option from the following statements :

1. Males do not suffer from colour blindness as the male gametes contain only Y-chromosome.
2. Males have one X-chromosome and one Y-chromosome. So even if one X-chromosome has the defective gene of colour blindness, it would be insignificant.
3. Their son may be colour blind, if he receives the X-chromosome with the defective gene from his mother.
4. None of these.

(i) Both (2) and (3)

Reason — Colour blindness is caused by a recessive allele. The gene is present only on the X-chromosome, not on all sex chromosomes. It is more common in males because males have only one X-chromosome.

(ii) The daughter has a normal vision without the defective gene on the chromosomes.

(iii) Their son may be colour blind, if he receives the X-chromosome with the defective gene from his mother.