Question

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

Answer 1

=
`(1)/(4)`

Step-by-step 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 =
`(1)/(2)`

So if a carrier woman cross with a normal man

Let say the gene of the carrier woman is:
`XX^c`

and the normal man =
`XY`

so if we have a cross between
`XY` and
`XX^c`; we have:

`X`
`Y`

`X`
`XX`
`XY`

`X^c`
`XX^c`
`X^cY`

we can see the offspring to be :

`XX` =normal unaffected female

`XY` = normal unaffected male

`XX^c` = carrier female for color-blind

`X^cY` = carrier male for color-bind

Then probability that of inheriting defective allele =
`(2)/(4)` =
`(1)/(2)`

Let's not forget that the probability that the woman is a carrier of color-blind allele is =
`(1)/(2)`

∴ the probability that the son is colorblind =
`(1)/(2)*(1)/(2)`

=
`(1)/(4)`