May 2003
Volume 44, Issue 13
ARVO Annual Meeting Abstract  |   May 2003
Ratio of L:M Cones in Males of African Descent
Author Affiliations & Notes
  • C. McMahon
    Cellular Biology Dept., Medical College of Wisconsin, Milwaukee, WI, United States
  • S. Awua
    Cellular Biology Dept., Medical College of Wisconsin, Milwaukee, WI, United States
  • J. Neitz
    Cellular Biology Dept., Medical College of Wisconsin, Milwaukee, WI, United States
  • M. Neitz
    Dept. of Ophthalmology, Medical College of Wisconsin, Milwaukee, WI, United States
  • Footnotes
    Commercial Relationships  C. McMahon, None; S. Awua, None; J. Neitz, None; M. Neitz, None.
  • Footnotes
    Support  Supprt: NIH grants EY09303, EY09620, EY01931 and RPB.
Investigative Ophthalmology & Visual Science May 2003, Vol.44, 1908. doi:
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    • Get Citation

      C. McMahon, S. Awua, J. Neitz, M. Neitz; Ratio of L:M Cones in Males of African Descent . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1908.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract: : Purpose: Among Caucasian males it has been estimated that the ratio of long (L) to middle wavelength (M) sensitive cones in the central retina averages ca. 2:1. A stochastic mechanism has been proposed to be responsible for the choice of a cone photoreceptor to express an L versus an M photopigment gene. In each cell a stable and permanent complex is hypothesized to form between a unique locus control region (LCR) 5' of the X-chromosome pigment gene array and the promoter of a randomly chosen gene in the array. Normal arrays have an L gene first (5'-most), followed by M genes, so the L gene is physically closest to the LCR. This has led to the hypothesis that the proximity of the LCR to the L gene promoter makes it more likely to bind the LCR and thus be selected for expression. The preponderance of L cones has been taken as strong evidence in favor of this hypothesis. If proximity to the LCR is a fundamental determinant of the probability of expression, then ethnic populations with the same array structure found in Caucasians should have a similar distribution and average ratio of L:M cones. We tested this prediction. Methods: L:M cone ratios were estimated using the flicker photometric electroretinogram (ERG). Subjects were African (n=13) and African-American (n=14) males, ages 15 to 43 years, with normal color vision. Each subject's X-chromosome pigment gene array was characterized by standard molecular methods. Results: All subjects had an L gene in the first position of their array. The African and African-American populations were not significantly different in L:M ratio. The range of variation in cone ratio in males of black African descent versus Caucasians was similar, however the mean ratio for subjects of African descent (1.27 L:1 M) was significantly different from the mean (1.9 L:1 M) previously estimated for Caucasians. Conclusions: These results suggest that a strong bias for expression of the first gene in the array is not a fundamental characteristic of the mechanism that determines whether a cone will be M or L. If it were, males of black African descent and Caucasians would be expected to have a similar bias in L:M ratio.

Keywords: color pigments and opsins • color vision • gene/expression 

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