If both parents of a male child are normal, what are the chances of the child being colour blind?

Question

If both parents of a male child are normal, what are the chances of the child being colour blind? (A) It is impossible (B) It is possible only if father’s mother was colour blind. (C) It is possible only if mother’s father was colour blind. (D) It is possible even when all the four grandparents had normal vision.

Tardigrade Admin · Accepted Answer

Colour blindness is the defect of colour vision in humans due to deficiency or absence of one of three visual pigments. This is due to a recessive gene carried on the X chromosome and therefore, men are more likely to show the defect although women may be carriers. Therefore, the genes of colour blindness are transferred from father to daughter and from daughter to her son. This is termed as criss-cross inheritance. Sons receive these characters from mother only while daughters receive from mother and father both.

Q. If both parents of a male child are normal, what are the chances of the child being colour blind?

It is impossible

It is possible only if father’s mother was colour blind.

It is possible only if mother’s father was colour blind.

It is possible even when all the four grandparents had normal vision.