Editing Color blindness (section)

===Genetics===
{{unreferenced section|date=May 2023}}

Color blindness is typically an inherited genetic disorder. The most common forms of color blindness are associated with the [[Photopsin]] genes, but the mapping of the human genome has shown there are many causative mutations that do not directly affect the opsins. Mutations capable of causing color blindness originate from at least 19&nbsp;different chromosomes and 56&nbsp;different genes (as shown online at the [[Online Mendelian Inheritance in Man]] [OMIM]).

====Genetics of red–green color blindness====
{{main|Congenital red–green color blindness#Genetics}}
[[File:Punnett square colour blindness.svg|thumb|alt=A chart showing likelihoods of genetic combinations and outcomes for red–green color blindness|Punnett squares for each combination of parents' color vision status giving probabilities of their offsprings' status; A superscript 'c' denotes a chromosome with an affected gene.]]
By far the most common form of color blindness is [[congenital red–green color blindness]] (Daltonism), which includes protanopia/protanomaly and deuteranopia/deuteranomaly. These conditions are mediated by the [[OPN1LW]] and [[OPN1MW]] genes, respectively, both on the [[X chromosome]]. An 'affected' gene is either missing (as in Protanopia and Deuteranopia - [[Dichromacy]]) or is a [[chimeric gene]] (as in Protanomaly and Deuteranomaly).

Since the [[OPN1LW]] and [[OPN1MW]] genes are on the X&nbsp;chromosome, they are [[Sex linkage|sex-linked]], and therefore affect males and females disproportionately. Because the color blind 'affected' [[alleles]] are recessive, color blindness specifically follows [[X-linked recessive inheritance]]. Males have only one X&nbsp;chromosome (XY), and females have two (XX); Because the male only has one of each gene, if it is affected, the male will be color blind. Because a female has two alleles of each gene (one on each chromosome), if only one gene is affected, the dominant normal alleles will "override" the affected, recessive allele and the female will have normal color vision. However, if the female has two mutated alleles, she will still be color blind. This is why there is a disproportionate prevalence of color blindness, with ~8% of males exhibiting color blindness and ~0.5% of females.

====Genetics of blue–yellow color blindness====
Congenital blue–yellow color blindness is a much rarer form of color blindness including tritanopia/tritanomaly. These conditions are mediated by the [[OPN1SW]] gene on [[Chromosome 7]] which encodes the S-opsin protein and follows autosomal dominant inheritance.<ref name="Sharpe1999"/> The cause of blue–yellow color blindness is not analogous to the cause of red–green color blindness, i.e. the peak sensitivity of the S-opsin does not shift to longer wavelengths. Rather, there are 6 known point mutations of OPN1SW that degrade the performance of the S-cones.<ref name="RCM2020">{{cite book |last1=Rodriguez-Carmona |first1=Marisa |last2=Patterson |first2=Emily J. |chapter=Photoreceptors, Color Vision |title=Encyclopedia of Color Science and Technology |date=2020 |pages=1–7 |doi=10.1007/978-3-642-27851-8_277-3 |isbn=978-3-642-27851-8 |s2cid=226504635 |chapter-url=https://openaccess.city.ac.uk/id/eprint/23584/1/Photoreceptors%20Color%20Vision_submitted%20to%20CRO.pdf |access-date=18 December 2023 |archive-date=2 December 2023 |archive-url=https://web.archive.org/web/20231202184422/https://openaccess.city.ac.uk/id/eprint/23584/1/Photoreceptors%20Color%20Vision_submitted%20to%20CRO.pdf |url-status=live }}</ref> The OPN1SW gene is almost invariant in the human population. Congenital tritan defects are often progressive, with nearly normal trichromatic vision in childhood (e.g. mild tritanomaly) progressing to dichromacy (tritanopia) as the S-cones slowly die.<ref name="RCM2020"/> Tritanomaly and tritanopia are therefore different penetrance of the same disease, and some sources have argued that tritanomaly therefore be referred to as incomplete tritanopia.<ref name="Sharpe1999">{{cite book |last1=Sharpe |first1=LT |last2=Stockman |first2=A |last3=Jägle |first3=H |last4=Nathans |first4=J |title=Color vision: From genes to perception |date=1999 |page=351 |url=http://www.cvrl.org/people/stockman/pubs/1999%20Genetics%20chapter%20SSJN.pdf |chapter=Opsin genes, cone photopigments, color vision, and color blindness. |quote=True cases of tritanomaly, as distinct from partial or incomplete tritanopia, have never been satisfactorily documented. Although the separate existence of tritanopia and tritanomaly, with different modes of inheritance, has been postulated, it now seems more likely that tritanomaly does not exist, but rather has been mistaken for incomplete tritanopia. |access-date=16 December 2023 |archive-date=3 October 2024 |archive-url=https://web.archive.org/web/20241003080812/http://www.cvrl.org/people/stockman/pubs/1999%20Genetics%20chapter%20SSJN.pdf |url-status=live }}</ref>

====Other genetic causes====
Several inherited diseases are known to cause color blindness, including [[achromatopsia]], [[cone dystrophy]], [[Leber's congenital amaurosis]] and [[retinitis pigmentosa]]. These can be [[congenital]] or commence in childhood or adulthood. They can be static/stationary or [[Progressive disease|progressive]]. Progressive diseases often involve deterioration of the retina and other parts of the eye, so often progress from color blindness to more severe [[visual impairment]]s, up to and including total blindness.