In pedigree analysis,the symbol given for sex unspecified is

$A$ normal woman whose father was colourblind marries a normal man. What kinds of children would be expected and in what proportion?

Identify the genotype of the first generation $(I)$ for an autosomal recessive disorder based on the provided pedigree chart.

Assertion: Persons suffering from haemophilia fail to produce blood clotting factor $VIII$.
Reason: Prothrombin producing platelets in such persons are found in very low concentration.

Assertion: Phenylketonuria is a recessive hereditary disease caused by the body's failure to oxidize the amino acid phenylalanine to tyrosine due to a defective enzyme.
Reason: It results in the presence of phenylalanine acid in urine.

$A$ normal-visioned man whose father was colourblind marries a normal woman whose father was also colourblind. They have one son. What is the probability of the son being colourblind (in $\%$)?