Which of the following is not true regarding haemophilia?

Which of the following is a sex-linked character?

Both husband and wife have normal vision,though their fathers were colourblind and mothers did not have any gene for colour blindness. The probability of their daughter becoming colourblind is

Sickle cell anaemia is caused due to the substitution of

Which of the following diseases belongs to the same category as colourblindness in man?

$A$ normal-visioned man,whose father was color-blind,marries a woman whose father was also color-blind. What is the probability that their first child,a daughter,will be color-blind (in $\%$)?