Why is colour blindness less common in women?<\/p>\n
Colour blindness occurs in around 8% of the male European population, and around 0.5% of female Europeans. This inequality is due to the association of colour blindness with the X chromosome.<\/p>\n
Humans see colour using three different proteins which each react to different wavelengths of light. These proteins are called opsins, and they come in forms which respond to red, green or blue light. Colour blindness is generally caused by a mutation in one or more of the genes encoding these proteins. Depending on the specific mutation, this may produce a non-functional opsin (resulting in dichromacy) or an opsin that does not react to the specific wavelengths that it is supposed to (anomalous trichromacy). The most common form is deuteranomaly, which is caused by a mutation of the green opsin, and affects red-green discrimination.<\/p>\n
The genes encoding the red and green opsin are located next to each other on the X chromosome, while the blue opsin gene is found on chromosome 7. This means that females carry two copies of the red and green opsin genes, while males only have one of each. Males with a mutation in one of these genes will exhibit colour blindness to some degree. Females, on the other hand, will only be colour blind if they carry mutations in both copies of one of the genes, which has a much lower chance of occurring.<\/p>\n