Editing Squirrel monkey (section)

=== Colour vision ===
{{See also|Evolution of colour vision in primates}}
[[Colour vision]] in squirrel monkeys has been extensively studied as a stand-in for human ailments.<ref name="Neitz">{{Cite journal|last1=Mancuso|first1=Katherine|last2=Hauswirth|first2=William W.|last3=Li|first3=Qiuhong|last4=Connor|first4=Thomas B.|last5=Kuchenbecker|first5=James A.|last6=Mauck|first6=Matthew C.|last7=Neitz|first7=Jay|last8=Neitz|first8=Maureen|author8-link= Maureen Neitz |date=2009-09-16|title=Gene therapy for red–green colour blindness in adult primates|journal=Nature|language=En|volume=461|issue=7265|pages=784–787|doi=10.1038/nature08401|pmid=19759534|issn=0028-0836|pmc=2782927|bibcode=2009Natur.461..784M}}</ref> In humans, two [[gene]]s for colour vision are found on the [[X chromosome]]. Typically, one gene ([[OPN1LW]]) produces a pigment that is most sensitive to the 564&nbsp;nm [[wavelength]], while the other gene ([[OPN1MW]]) produces a pigment most sensitive to 534&nbsp;nm. In squirrel monkeys, there is only one gene on the X chromosome but it exists in three varieties: one is most sensitive to 538&nbsp;nm, one to 551&nbsp;nm, and one to 561&nbsp;nm. Since males have only one X chromosome, they are [[dichromacy|dichromatic]], although with different sensitivities. Females have two X chromosomes, so some of them can have copies of two different [[allele]]s. The three alleles seem to be equally common, leading to one-third of females being dichromatic, while two-thirds are [[trichromatic]].<ref>{{cite journal|pmc=304691 | pmid=3470811 | volume=84 | issue=8 | title=Inheritance of color vision in a New World monkey (Saimiri sciureus) |date=April 1987 | journal=Proc. Natl. Acad. Sci. U.S.A. | pages=2545–9 |vauthors=Jacobs GH, Neitz J | doi=10.1073/pnas.84.8.2545| bibcode=1987PNAS...84.2545J | doi-access=free }}</ref> Recently, [[gene therapy]] has given the human OPN1LW gene to adult male squirrel monkeys, producing behaviour consistent with trichromatic colour vision.<ref name="Neitz"/>