Genetic counsellors can identify heterozygous individuals by

$A$ normal woman,whose father was color-blind,marries a normal man. What will be the status of their sons?

Which of the following disorders is more commonly observed in males than in females?

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.

Select the incorrect match regarding the symbols used in Pedigree analysis:

$A$ colour blind man marries a woman with normal sight who has no history of colour blindness in her family. What is the probability of their grandson being colour blind?