(a) her mother and maternal grandfather were colourblind
(b) her father and maternal grandfather were colourblind
(c) her mother is colour blind and father has normal vision
(d) parents have normal vision but grand parents were colourblind
[CBSE AIPMT 1991]
Correct Option (b) Reason : For a girl to be colourblind, the genotype of her father should be Xᶜ Y and of her mother either Xᶜ X or Xᶜ Xᶜ, where Xᶜ represents colour blind gene.
In the given options this is only possible when her father and maternal grandfather were colour blind.