If a women who is heterozygote for color-blindness married to a color-blind man with normal vision,the probability that her daughter is color blind is:
a.0%
b.25%
c.50%
d.75%
e.100%

Question

If a women who is heterozygote for color-blindness married to a color-blind man with normal vision,the probability that her daughter is color blind is:
a.0%
b.25%
c.50%
d.75%
e.100%

rushwr · Answer

it's going to be 50% answer C. Colourblindness is  recessive. 
Parental genotypes  are going to be $$X ^{C}X ^{c}  $$ from mother and $$X ^{c}Y$$ from mother. Here there are @ sons and @ daughters. Nut out of the 2 daughters one will be colour blind and the other one will be heterozygote. Hence we take it as 50%

anonymous · Answer

@rushwr It is not just because it is recessive.  The gene(s) involved are only on the X chromosome.  Males only have 1 X chromosome so if they have faulty gene(s) they will always pass this along to their daughter.  Females have 2 X chromosomes and now the dom/res gene thing comes into play.

rushwr · Answer

yeah that is not what I meant ! Isn't it a fact that all the sex linked disorders involves X chromosomes only.

anonymous · Answer

@Rushwr There are some Y linked diseases.  Most are not terrible because those usually die out as all men with it would be affected.   You still need to know both if it is dom/res and the relationship with the sex chromosomes.  If it was a dominant mutation then all the daughters of the couple would have it, despite the heterozygocity of the mother.  Since it is now, only 50% will.

anonymous · Answer

thanks @Rushwr @mrdoldum