Human Molecular Genetics, 2002, Vol. 11, No. 1 23-32
© 2002 Oxford University Press
The molecular basis of dichromatic color vision in males with multiple red and green visual pigment genes
1Department of Neuro-Ophthalmology, University Eye Hospital, Roentgenweg 11, D-72076 Tübingen, Germany, 2Departments of Medicine and Genome Sciences, University of Washington, Seattle, WA, USA and 3Department of Psychology, University of Newcastle, Newcastle-upon-Tyne NE1 7RU, UK
We investigated the genotypic variation in 50 red–green color vision deficient males (27 deuteranopes and 23 protanopes) of middle European ancestry who possess multiple genes in the X-linked photopigment gene array. We have previously shown that only the first two genes of the array are expressed and contribute to the color vision phenotype. Therefore, the hypothesis is that the first two genes possessed by multigene-dichromats encode pigments of identical or nearly identical spectral sensitivity: one gene normal (R or G) and the other a hybrid (G/R or R/G). The spectral sensitivities of the encoded pigments were inferred from published in vitro and in vivo data. The color vision phenotype was assessed by standard anomaloscopy. Most genotypes (92%) included hybrid genes whose sequence and position and whose encoded pigment correlated exactly with the phenotype. However, one and possibly two of the protanopes had gene arrays consistent with protanomaly rather than protanopia, since two spectrally different pigments may be encoded by their arrays. Two of the deuteranopes had only R- and G-photopigment genes, without any detectable G/R-hybrid genes or any as-of-yet identified point mutation or coding/promoter sequence deletions. Further, an unexpectedly high number of multigene-deuteranopes (11%) had the C203R mutation in their most upstream G-pigment gene, suggesting a founder effect of middle European origin for this mutation. About half of the protanopes possessed an upstream R/G-hybrid gene with different exon 2 coding sequences than their downstream G-pigment gene(s), which is inconsistent with published data implying that a single amino acid substitution in exon 2 can confer red–green color discrimination capacity on multigene-protans by altering the optical density of the cones.
+ To whom correspondence should be addressed at: Department of Psychology, University of Newcastle, Newcastle-upon-Tyne NE1 7RU, UK. Tel: +44 191 2227514; Fax: +44 191 2225622; Email: l.t.sharpe@ucl.ac.uk Correspondence may also be addressed to S. S. Deeb at: Departments of Medicine and Genome Sciences, Box 357360 (Room 206), University of Washington, Seattle, WA, USA. Tel: +1 206 543 1706; Fax: +1 206 543 0754; Email: deeb@genetics.washington.edu
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