Colour blindness is caused by a single

The given diagram $A$ and $B$ indicates:

What does the given symbol represent?

Given below are two statements:
Statement $I$: The son of a carrier woman has a $100$ percent chance of being colour blind.
Statement $II$: $A$ daughter of a carrier mother and a normal father will be $100$ percent colour blind.
In the light of the above statements,choose the correct answer from the options given below:

Which of the following diseases belongs to the same category as colourblindness in man?

Colour blindness is