Red-green colour blindness is a sex-linked recessive disorder caused by a gene on the X chromosome…

Genotypes. The woman has normal vision, but her father passed her his $X^c$, so she is a carrier, $X^CX^c$. The man is $X^cY$.

(a) Daughters. Every daughter gets $X^c$ from her father. From her mother she gets $X^C$ or $X^c$, each with a chance of $\frac{1}{2}$. So $50\%$ of the daughters are $X^cX^c$, colour blind.

(b) Sons. A son gets the Y from his father and one of his mother's X chromosomes, so $50\%$ of the sons are $X^cY$, colour blind. This is the son of a carrier woman having a $50$ per cent chance of being colour blind.

(c) A colour-blind daughter first. The chance of a daughter is $\frac{1}{2}$, and of her being colour blind $\frac{1}{2}$: $\dfrac{1}{2} \times \dfrac{1}{2} = 25\%$.

(d) A normal daughter. She has the father's $X^c$, so to have normal vision she must have the mother's $X^C$: she is $X^CX^c$, a carrier, with a chance of $100\%$.

(e) Two normal sons. Each son has normal vision with a chance of $\frac{1}{2}$: $\dfrac{1}{2} \times \dfrac{1}{2} = 25\%$.