An example of a disease caused by a molecular mutation is

In a cross between a male and female, both heterozygous for sickle cell anaemia gene, what percentage of the progeny will be diseased? (In $ \%$ )

Select the incorrect statement with regard to haemophilia.

Why is the frequency of red-green colour blindness many times higher in males than in females?

$A$ normal-visioned man whose father was colourblind marries a normal woman whose father was also colourblind. They have one son. What is the probability of the son being colourblind (in $\%$)?

$A$ - Sickle-cell anaemia is a sex-linked recessive trait.
$R$ - This disease is controlled by more than two pairs of alleles.