Can Women Be Colourblind?

Mystery Hour Question

I'm coloublind and yesterday my daughter went to an eye test and asked if she could be colourblind. She was told no, because only men are colourblind. Is that true and if so, why?
Terry, Harlow

Answer

** Definitive **
Name: Lucy, Chelmsford
Qualification: Mother
Answer: My daughter's nursery were worried that she wasn't learning her colours. She has astigmatism and is long sighted anyway, so she already wears glasses. I took her to the optician and explained the problem and they said it's possible that she's colour-blind, but it's extremely rare in girls. It has to be on both sides of the family to happen.

Name: Claire, Frankfurt
Qualificaiton: Paid attention in biology (and also a Mum!)
Answer: It's to do with chromosomes. Men have the XX chromosomes, while women have XY. If colourblindness only attached itself to the X chromosone, that would make it much more likely for men to have it than women.

Name: Obinna
Qualification: Medical student
Answer: The answer above is wrong: it is the men who are XY and females are XX. The mutated gene responsible for colourblindness does attach itself to the X chromosome and the reason males are at a greater risk of inheriting an X linked mutation is because males only have one X chromosome (XY, with the Y chromosome being significantly shorter than the X chromosome), and females have two (XX); if the women inherit a normal X chromosome in addition to the one which carries the mutation, they will not display the mutation, while men have no 'spare' normal chromosome to override the chromosome which carries the mutation.