M-cone opsin gene number does not correlate with variation in L/M-cone sensitivity.
Molecular genetic studies demonstrate that the human cone opsin gene array on the q-arm of the X-chromosome typically consists of one long-wave-sensitive (L) cone opsin gene and from one to several middle-wave-sensitive (M) cone opsin genes. Although the presence of the single L-cone opsin gene and at least one M-cone opsin gene is essential for normal red-green colour discrimination, the function of the additional M-cone opsin genes is still unclear. To investigate whether any variations in phenotype correlate with differences in the number of M-cone opsin genes, we selected 13 normal trichromat males, for whom four independent molecular techniques have exactly determined their number of M-cone opsin genes, ranging from one to four. Their phenotype was characterized by estimating their foveal L- to M-cone ratio from heterochromatic flicker photometric (HFP) thresholds, by measuring the wavelength corresponding to their 'unique yellow', and by determining their L- and M-cone modulation thresholds (CMTs). No correlation was found between these psychophysical measures and the number of M-cone opsin genes. Although, we found a reasonably good correlation between the L/M-cone ratios based on HFP and on CMT, we did not find any correlation between the estimated L/M-cone ratios and the settings of 'unique yellow'. Our results accord with previous molecular genetic studies that suggest that only the first two genes in the X-linked opsin gene array are expressed.
University Eye Hospital, FEO, 72076, Tübingen, Germany.
H
H
Knau
J
J
Kremers
H-J
HJ
Schmidt
S
S
Wolf
B
B
Wissinger
L T
LT
Sharpe
D003118:Color Perception / Q000235:genetics*; D005838:Genotype; D006801:Humans; D008297:Male; D010641:Phenotype; D010783:Photometry; D011601:Psychophysics; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D017299:Rod Opsins / Q000235:genetics*
D017299:Rod Opsins