Color blindness in a family tree & how is it passed on...?

Figure 1 A family tree showing the pattern of inheritance of colour vision
Deficiency.

(a) Explain what is meant by saying an individual is heterozygous for the colour
Vision gene, and why females can be heterozygous for colour deficiency in
This family but males cannot. (About 80 words)

(b) Study Figure 1 and then using the symbol 'XB' for the allele coding for
Normal colour vision and 'Xb' for the allele coding for colour vision
Deficiency, write down the genotypes for the colour vision gene for the
Following three grandparents in the family. In each case briefly state how you
Reached your conclusion (a few sentences). (Hint: you will have to consider
The phenotypes of all three generations to answer this question.)

' Alfred
' Diane
' Fiona

__________________________________________________ _______________

(c) Matthew and Paul are both baby boys, and it is too early to determine
Whether they have normal colour vision. Given the knowledge that they are
Male, calculate the statistical probability that:

(i) Matthew will have colour vision deficiency

(ii) Paul will have colour vision deficiency
In calculating your answers, you should include two genetic cross diagrams
For the parents of Matthew and Paul showing the genotypes and phenotypes
Of the parents and of all the possible offspring with respect to colour vision.