The 23rd chromosome is made up of two parts – either two X chromosomes if you are female or an X and a Y chromosome if you are male. The faulty ‘gene’ for colour blindness is found only on the X chromosome. So, for a male to be colour blind the faulty colour blindness ‘gene’ only has to appear on his X chromosome. For a female to be colour blind it must be present on both of her X chromosomes.

If a woman has only one colour blind ‘gene’ she is known as a ‘carrier’ but she won’t be colour blind. When she has a child she will give one of her X chromosomes to the child. If she gives the X chromosome with the faulty ‘gene’ to her son he will be colour blind, but if he receives the ‘good’ chromosome he won’t be colour blind.

A colour blind boy can’t receive a colour blind ‘gene’ from his father, even if his father is colour blind, because his father can only pass an X chromosome to his daughters.

A colour blind daughter therefore must have a father who is colour blind and a mother who is a carrier (who has also passed the faulty ‘gene’ to her daughter). If her father is not colour blind, a ‘carrier’ daughter won’t be colour blind. A daughter can become a carrier in one of two ways – she can acquire the ‘gene’ from a carrier mother or from a colour blind father.

This is why red/green colour blindness is far more common in men than women.

Blue colour blindness affects both men and women equally, because it is carried on a non-sex chromosome.

the answer could be option 1

the answer is option 1 that is 25%