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Maureen Neitz, Jay Neitz; Evolution of opsins and inter-individual variability in humans. Journal of Vision 2006;6(13):35. doi: 10.1167/6.13.35.
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© ARVO (1962-2015); The Authors (2016-present)
In comparison to most other proteins and to other opsins, the human long-wavelength (L) and middle-wavelength (M) opsins exhibit and extraordinary degree of amino acid sequence variability. For example, sequence variability in human rhodopsin is quite low, and the variability that has been observed has, with rare exception, been associated with disease, including progressive retinal degeneration, and stationary night blindness. Likewise, variation in the human short-wavelength (S) sensitive opsin sequence is quite rare, and all variation observed has been associated with tritan color vision deficiency. Mutations in rhodopsin and the S cone opsin arise from extremely rare random mutational events. In contrast, the human M and L opsin genes are prone to unequal homologous recombination, as evidenced by the high incidence of color vision defects in modern populations and the high frequency of female carriers. Over the course of human evolution, sequential rounds of unequal homologous recombination between normal and color defective opsin gene arrays has produced the variability in the present day L and M opsins. Evidence has accumulated indicating that the mechanism that produces the hypervariability in L and M opsins is uniquely human and that it has dire consequences for the evolution of human vision.
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