Question

If a colour-blind woman marries a normal man, the chance that their boy child will be colour-blind is ........... %.

Hint:

Colour blindness is an X-linked recessive trait, and male children inherit their X chromosome from their mother. If the mother is colour-blind, all her sons will be colour-blind.

Answer 1

Correct Answer: 100

Step 1: Understanding the genetic inheritance of colour blindness. 
Colour blindness is an X-linked recessive trait. In a colour-blind woman, the genotype is X\(^c\)X\(^c\), where X\(^c\) represents the X chromosome carrying the colour-blind allele. The man, being normal, will have the genotype X\(^N\)Y, where X\(^N\) represents the normal X chromosome and Y is the male sex chromosome.

Step 2: Genetic inheritance for a son. 
Sons inherit their X chromosome from their mother and their Y chromosome from their father. Since the mother is colour-blind (X\(^c\)X\(^c\)), she can only pass on the X\(^c\) chromosome. The father, being normal, will pass on the Y chromosome. Thus, the son will inherit X\(^c\)Y, making him colour-blind.

Step 3: Conclusion. 
Since the son will always inherit the X\(^c\) chromosome from his colour-blind mother, he will be colour-blind. Therefore, the chance that their boy child will be colour-blind is 100%. The correct answer is 100.