Color vision occurs because the retina of the human eye
has both rod cells, which distinguish light in general, and cone cells, which are highly
sensitive only to specific wavelengths. While there are three groups of peak wavelength
sensitivity, any given cone cell will only respond to a single peak. This occurs because
the cone cell is rich in a pigment which is sensitive to decomposition at a single
wavelength.
Different genes code for the different
pigments, but all the genes are located on the X chromosome. There are several common
mutations known, each of which causes one of these genes to be unable to code for
proteins which produce a functional pigment. These genes are recessive, so a person
carrying a defective gene can, if they have a second, correct copy of the gene, still
make the pigment. This is true in females, who can thus be carriers. However in males,
who have one X and one Y chromosome, there is only one version of each of the pigment
encoding genes present. If it is defective, the person is color
blind.
Consequently, color blindness is not a disease, and
cannot be cured. At present no way has been found to induce an affected person's retinal
cells to produce correctly formed pigment molecules. Since the pigments must be produced
constantly and are only found in the cones of the retina there is no practical method of
providing these molecules as supplements. Perhaps at some point in the future gene
therapy will be available to remedy this common genetic problem.
No comments:
Post a Comment