Friday, November 26, 2010

Life Lines 55


Almost all mammals can see yellow and blue which is associated with a gene that is not on a sex chromosome. In humans a mutation of the yellow-blue gene results in vision that sees only black and white, like movies or TV sets in an earlier generation. Mammals also see green. The genes involved produce proteins called opsins, which are sensitive to color. In African primates a duplication of the green opsin gene occurred and eventually mutated to become sensitive to longer wavelengths we associate with red. We humans thus have three opsin genes – for the yellow-blue, the green, and the red. Persons who are color deficient are usually defective for the green or red opsin gene an event that happens relatively frequently because the red and green genes are tandem duplications and frequently mispair leading to a product that may be defective for the red or green opsin gene. An eye doctor can readily tell, by using color charts, whether a colorblind person has a mild or severe loss of the green or red gene.

Mice, like most mammals, have the green and the yellow-blue genes. They do not see red. Scientists at Johns Hopkins University and at Santa Barbara inserted a gene for the red opsin gene into a fertilized egg of a mouse and bred the resulting mouse and its offspring to produce a strain of mice with the red opsin gene present. They then tested the mice using red or green plastic levers to release food when pressed, a standard animal psychology approach. The modified mice could recognize the red lever and distinguish it from green, but control mice could not, with both the red and the green levers appearing identical. This demonstrated that the mammalian brain is capable of learning new experiences never encountered before. They could interpret new wavelengths (which we see as red) and respond in a similar way to people who are not colorblind. The capacity to see red (or presumably any color) is a matter of the wavelength sensitivity of the opsin genes present.

Theoretically humans could do the same thing to themselves, and it might be possible to add the red or green opsin gene to a human zygote after fertilization and instead of a color-blind boy (the trait is X-linked in humans) the child might have normal color vision. It is also possible that opsin-like genes present in butterflies and bees, which recognize ultraviolet as a color, might be added and we could extend our color range. Similarly, the red-opsin gene could be altered and added to allow some people to see infrared and greatly increase their night vision. Genetic manipulation is not yet a precise science and lots of risks may abound from inserting genes in inappropriate places. For those who fantasize those problems will be solved and who want the benefits of such genetic manipulation, consider the possible disruption in sleeping patterns and the inability to get rid of distractions like the warm bodies glowing in a dark room (a theatre or movie house) or the persistent images of warm objects (like radiators or hot water pipes in the walls) while you try to sleep. Extending our color range by adding opsin genes may lead to a Midas touch of surfeit color.

No comments: