A normal woman, whose father was colour-blind is married to a normal man. The sons would be
All normal
All colour-blind
$75\%$ colour-blind
$50\%$ colour-blind
What is the cause of haemophilia
Recessive characters are expressed
Given below is a pedigree chart of a family with five children. It shows the inheritance of attached earlobes as opposed to the free ones. The squares represent the male individuals and circles the female individuals Which one of the following conclusions drawn is correct
Haemophilia $A$ is due to the absence of