Abstract
PURPOSE: A deuteranope's mother and daughter are obligate carriers of deuteranopia, who have one defective and (in most cases) one normal X chromosome. The normal array has both L- and M-photopigment genes (L1 and M1); the defective array has an L-photopigment gene (L2), which is not necessarily the same as the L1 in the normal array. According to Lyonization (Lyon, 1961), a female carrier's defective gene is expressed so she may have more than two types of L/M photopigments (for example, L1, M1 and L2). An open question is how a deuteranopic carrier's third pigment in the L/M range (L2) contributes to the neural signals encoding color. Carriers' Rayleigh matches are known to have a midpoint within the normals' match range; and carriers' Rayleigh-match range can be normal or enlarged (Pickford, 1944; Krill & Schneiderman, 1964; Jordan & Mollon, 1993). Here, a model considered how the signal from cones with the L2 pigment pools with the signal from cones with the L1 or M1 pigment. The model predicted individual differences in Rayleigh-match midpoint and range for carriers of deuteranopia.
METHODS: The model determined carriers' Rayleigh matches based on three different assumptions about the signal from cones with the L2 pigment: it pools with the signal from cones with (1) only the M1 pigment, (2) only the L1 pigment or (3) either the M1 or L1 pigment, unselectively. L2 spectral-sensitivity peak, L2 optical density, and the relative number of L1, L2 and M1 cones were varied in the model.
RESULTS AND CONCLUSIONS: The model predicted typical deuteranopic carriers' matches (that is, midpoint within the color normals' range and match range normal or enlarged) only under the assumption that the signal from cones with the L2 pigment pools unselectively with the L1- and M1-cone signals.
Supported by NIH grant EY-04802.