What will be the probability of having the colour-blind

Home » Genetics Ⅰ » Genetics-i Miscellaneous » Question

Direction: Red-green colour blindness is inherited as a recessive X-linked trait.

What will be the probability of having the colour-blind daughter to a phenotypically normal woman, who already had one colour-blind son, and is married to a colour-blind man?

1. 75 %
2. 50 %
3. 25 %
4. 15 %

Correct Option: B

Let say woman can be a carrier or normal and married to a colorblind man.
So, woman can be either X^RX or XX and man is X^RY
Therefore, X^RX * X^RY and XX * X^RY

X^R X	X X
X^R X^RX^R X^RX	X^R X^RX X^RX
Y X^RY XY	Y XY XY

Therefore, out of 4 children, there is only one chance of having a colorblind daughter.
The probability for 1 out 4 children = ¼ = 0.25 = 25% ;
Now there are 2 probable daughters.
Probability for daughter to be colorblind = ½ = 50%