A normal couple has seven children (2 daughters and 5 sons). Three of the sons suffer from a hereditary disorder but none of the daughters is affected. Which is the inheritance type
1. Sex-limited recessive
2. Autosomal dominant
3. Sex-linked dominant
4. Sex-linked recessive.

If a colourblind man marries a woman who is homozygous for normal colour vision, the probability of their son being colourblind is:

1. 0

2. 0.5

3. 0. 75

4. 1