Which one of the following is a sex-linked trait?

Give differences: Haemophilia and Sickle-cell Anaemia.

$A$ man with normal vision whose father was colourblind marries a woman whose father was also colourblind. Suppose their first child is a daughter,what are the chances of this child being colourblind (in $\%$)?

$A$ husband and wife both have normal vision,although both of their fathers were colorblind. What is the probability that their daughter will be colorblind (in $\%$)?

Given that $X^h$ is the chromosome with the gene for haemophilia and $X$ is the chromosome with the normal gene. Which of the following individuals will act as a carrier for haemophilia?

Give scientific reasons: The product of phenylalanine catabolism excreted in the urine in phenylketonuria.