OPN1MW2

OPN1MW2 is a duplication of the OPN1MW gene, which encodes the medium wavelength sensitive (MWS) photopsin.

OPN1MW2 is a duplication of the OPN1MW gene arising from unequal homologous recombination.

Carriers will have one opsin gene (OPN1MW or OPN1LW) with differing alleles thereof on each chromosome, such that the alleles encode proteins with different spectral sensitivities.

Both of these alleles are expressed due to x-inactivation (one kind of X chromosome will get expressed in some photoreceptor cells, whereas the other kind of X chromosome will get expressed in the other photoreceptor cells) so a carrier will have 4 distinct cones with different spectral sensitivities, which is one prerequisite of tetrachromacy.

Therefore the OPN1MW2 gene is not considered a likely candidate mechanism for tetrachromacy.

Unequal homologous combination that leads to gene deletion and therefore underlies congenital dichromacy (protanopia and deuteranopia). The third gene array shows a deuteranopia genotype; the fourth shows a normal color vision genotype.