Question

A colour-blind mother and normal father would have

• A. Colour blind sons and daughters
• B. Colour blind sons and normal/carrier daughters
• C. All normal
• D. All colour blind

Hint:

Color blindness is a sex-linked recessive trait carried on the X chromosome. Males with the allele will express the condition, while females need two copies of the allele to be affected.

Answer 1

The Correct Option is B

Color blindness is an X-linked recessive trait. The gene responsible for color blindness is located on the X chromosome. Since males only have one X chromosome, a single recessive allele (X^c) on the X chromosome will cause color blindness. Females have two X chromosomes, so a female must inherit two copies of the color-blind allele (X^c) to be color blind.

(1) In this case, the mother is color blind and has the genotype X^cX^c. The father is normal and has the genotype X^Y.

(2) Sons inherit their Y chromosome from their father and one X chromosome from their mother. Since the mother can only provide a color-blind X chromosome (X^c), all the sons will be color blind (X^cY).

(3) Daughters inherit one X chromosome from each parent. The father provides a normal X chromosome (X), and the mother provides a color-blind X^c chromosome. Thus, the daughters will either be normal (XX) or carriers (X^cX), but not color blind.

Conclusion: The offspring of a color-blind mother and a normal father will have color-blind sons and normal/carrier daughters.