Question

Both the husband and wife have normal vision. The wife gives birth to a colour-blind daughter.
Is it more likely that the father is colour blind or has normal vision? What does this lead you
to deduce about the girl’s parents genome?

Answer 1

Since colourblindness is an X-linked recessive trait.

Since father has normal vision, therefore the genotype of father = XY

mother has normal vision, therefore the genotype of mother could be XXc or XX

Now if the genotype of mother is XX and genotype of father is XY

Therefore XX x XY

Gametes --------> X X Y

offsprings --------->    XX (Normal female) XY (Normal male)

Now if the genotype of mother is XXc and father is XY

Therefore X Xc x XY

Gametes --------> X Xc   X Y

offsprings ---------> XX XXc    XY XcY

  (Normal female) (Carrier female) (Normal male) (colorblind male)

From the above crosses, it can be concluded that from two normal parents or from carrier mother and normal father, colourblind daughter is not possible.

this is possible only when both parents have the colour blind allele (carrier mother and colourblind father).

Therefore the genotype of paents cannot be predicted.