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

Why are thalassemia and haemophilia categorised as Mendelian disorders? Write the symptoms of these diseases. Explain their pattern of inheritance in humans.

If a colour blind lady marries a normal man, their children will be

A normal­visioned man whose father was colour­ blind, marries a woman whose father was also colour­blind. They have their first child as a daughter. What are the chances that this child would be colour­ blind ?