The blackening of urine when exposed to air is a metabolic disorder in human beings. This is due to the presence of:

Pedigree analysis is $NOT$ useful for which of the following purposes?

$A$ colourblind daughter is born when:

$A$ woman carrying two genes for haemophilia and one gene for colour blindness on one of her $X$ chromosomes marries a normal man. What will be the phenotype of the progeny?

$A$ 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 $\%$)?

One of the genes present exclusively on the $X$-chromosome in humans is concerned with