Question

A colourblind man marries a carrier woman. The percentage of their colourblind progeny in the next generation will be ____

• A. 75\%
• B. 100\%
• C. 25\%
• D. 50\%

Hint:

X-linked recessive traits like colourblindness show a 50\% chance of affected offspring when a carrier female mates with an affected male.

Answer 1

The Correct Option is D

• Genetics of Colourblindness: Colourblindness is an X-linked recessive trait. Let $X^B$ be the normal allele and $X^b$ be the colourblind allele.
  • Colourblind man: $X^bY$
  • Carrier woman: $X^BX^b$ (has one normal and one colourblind allele)
• Punnett Square:

  	$X^B$	$X^b$
  $X^b$	$X^BX^b$ (carrier female)	$X^bX^b$ (colourblind female)
  $Y$	$X^BY$ (normal male)	$X^bY$ (colourblind male)

• Progeny Analysis:
  • 25% carrier females ($X^BX^b$)
  • 25% colourblind females ($X^bX^b$)
  • 25% normal males ($X^BY$)
  • 25% colourblind males ($X^bY$)
  • Total colourblind progeny = 25% (females) + 25% (males) = 50%.
• Option Analysis:
  • (1) 75%: Incorrect.
  • (2) 100%: Incorrect.
  • (3) 25%: Incorrect.
  • (4) 50%: Correct.
• Conclusion: The correct answer is (4) 50%.