The wavelengths of maximal sensitivity, as measured in the indicated studies, are given. Arrows representing exons 2 to 5 of genes for L-class and M-class pigments are similarly color coded. Black and white boxes indicate that amino acids specified at the spectrally active position are those that shift the spectra long and short, respectively. Codons 277 and 285 encode amino acids that determine whether the specified pigment is L or M. Codon numbers or amino acid positions for the spectral tuning sites are given. A, Exons 2 to 5 of the genes and the 7 spectral tuning sites they encode are shown (left). Spectral tuning of long-wavelength sensitive (L) and middle-wavelength sensitive (M) pigments. Vertical lines indicate 530 nm, near which M pigments cluster in peak sensitivity, and 560 nm, near which L pigments cluster in peak sensitivity. Protanomalous trichromats have 2 slightly different M pigments. Deuteranomalous trichromats have 2 slightly different L pigments. B, Anomalous trichromacy (deuteranomaly). The normal S, M, and L pigment spectra are shown. Dichromats have only 1 pigment in the L or M region of the spectrum. The degree of color vision deficiency in persons with anomalous trichromacy depends on the magnitude of the spectral difference between the pigment subtypes. Red-green color-deficient individuals are missing either all members of the L class or all members of the M class of pigment. Normal trichromats have at least 1 each of the short-, middle-, and long-wavelength sensitive classes of pigments, identified as S, M, and L. Photopigments underlying normal and defective red-green color vision are illustrated.
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