Causes of Colour Blindness Causes of Colour Blindness

Colour blindness is normally passed down from parents. The faulty gene is carried on the X chromosome (sex chromosome) which is the reason why men are affected more than women. 

We have 23 pairs of chromosome, the first 22 pairs are autosomes and the final pair are called the sex chromosome. These determine an individual’s sex: females have two X chromosomes (XX) and males have an X and a Y chromosome (XY).
So, for a male to be colour blind the faulty gene only has to appear on his X chromosome, for a female to be colour blind the faulty gene must appear in both of her X chromosomes.

If a woman has one faulty gene she is known as a carrier but she will not be colour blind. When she has a child she will give one of her X chromosomes to that child. If she gives the X chromosome with the faulty gene he will be colour blind. A colour blind boy cannot receive the faulty gene from his father because a father can only pass an X chromosome to his daughter.

For a colour blind daughter she must have a father who is colour blind and a mother who is a carrier, who has passed the faulty gene to her daughter.
A daughter can become a carrier in one of two ways:

1. From her carrier mother
2. From a colour blind father

If a woman inherits both of the faulty X chromosomes she will be colour blind herself and will pass on colour blindness to her sons.


Colour blindness Inheritence diagram. Img src:

See also:

What is Colour Blindness?

Anatomy of the Eye

Types of Colour Vision


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Read more:

American Academy of Opthalmology


Read more:

New Scientist - 21st March 2017

Daily Mail Online - 22nd March 2017

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