Why are more men colourblind than women?

Depending on where you look, it can either be one in eight men are colour vision deficient or one in twelve, but regardless of the stats, it is true more men have this condition than women. It occurs in only about 1 in 250 women. So that equates to about 95% of people who are colour vision deficient are men.
Why?
Well, it comes down to chromosomes and genetics which can get complicated. So buckle yourself in for an explanation.
Colour vision is passed along the genetic line through the x-chromosome. People with an x-chromosome and a y-chromosome only need their one x to be defective to catch it. People with two x-chromosomes need both to be defective. Clear as mud right – let’s try this from the beginning.
Men have one X chromosome and one Y chromosome, while women have two X chromosomes. To experience colour vision loss, the genetic mutation for colour blindness must be present on the X chromosome, but for women, this means it must be present on both X chromosomes. Men only need the mutation to be present on their singular X chromosome, making it much easier for them to inherit this colour vision loss.
To make this even more confusing this genetic mutation is passed down by parents. Though, even if neither parent is colour blind, it does not mean the child can’t be.
Genetics are hard right?
Women can be carriers of the gene without expressing it themselves. Mothers may have the mutation present on one X chromosome only, meaning she would not be colour blind, but can pass the gene down to the child.
Here’s an example – if the maternal grandfather was colourblind, this means his one X chromosome has the mutation, which is passed onto the daughter. The daughter receives another X chromosome from the maternal grandmother, but still, her colour vision will not be impacted. This makes her a carrier of the X chromosome with the colour blind mutation which can be passed on to her son(s). That is because a male child receives a Y chromosome from the father and an X chromosome from the mother. Then due to the mother having one mutated and one normal X chromosome, the male child will have a 50% chance of inheriting the colour blindness gene.
Hopefully these images help, but it is understandably confusing.

Genetics have a lot to answer for. That is the sole reason why men have colour vision deficits more often than women. Although there is no cure for colour blindness, our iRo lenses can help 95% of people with a colour vision deficit actually see new and more vibrant colours.