Color blindness or color vision deficiency affects about 2.7 million people in Britain. In many individuals, the condition is mild and a person is unaware there is a problem with their color perception until it is detected during a vision test. Other people, however, may notice that they see slightly different shades or hues of colors to those that other people see.
One of the most common forms of inherited color vision deficiency is the red–green deficiency or deuteranopia. This type of color blindness is passed on via the X chromosome and is more common in men who have only the one X chromosome, than in women, who have two X chromosomes. In men, the prevalence of color blindness is around 5.0% to 8.0%, while in women the prevalence is only 0.5% to 1.0%.
Since female offspring always receive one X chromosome from their mother and one from their father, a color blind father always transmits the gene for color blindness to any daughters he may have. These daughters then become carriers of the gene and have a 50% chance of passing the abnormal gene to their sons. A color blind man cannot transmit the condition to his male offspring, since the male always inherits the mother’s X chromosome.
In Australia, around 8.0% of the male population is color blind compared to around 0.4% of the female population.
In countries where there are isolated communities with limited gene pools, the prevalence may be increased, including that of the more rare forms. Examples of countries with such communities include rural areas of Hungary, Finland and some Scottish islands.
According to 2006 estimates from the Howard Hughes Medical Institute, around 7.0% of the male population and 0.4% of the female population cannot differentiate between red and green or they perceive red and green differently to other people. Overall, nearly all (95%) color vision deficiencies involve abnormal perception of red and green colors and it is uncommon for men or women to have difficulty perceiving the blue end of the color spectrum.