A woman with normal vision has a son. The woman’s maternal grandfather is color-blind. What is the probability that the son is colorblind, if his father is normal? Assume there are no other color-blind individuals in the pedigree. A. 1/2B. 1/3C. 1/4D. 1/6E. 1/8

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Explanation:

Given that the woman’s maternal grandfather is color-blind, then it is possible that the woman is a carrier of color-blind allele.

Then probability that the woman is a carrier of color-blind allele is =  

So if a carrier woman cross with a normal man

Let say the gene of the carrier woman is:

and the normal man =

so if we have a cross between   and ; we have:

we can see the offspring to be :

=normal unaffected female

= normal unaffected male

= carrier female for color-blind

= carrier male for color-bind

Then probability that of  inheriting defective allele = =

Let's not forget that the probability that the woman is a carrier of color-blind allele is =  

∴  the probability that the son is colorblind =

=