Coloring the World

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Basic Genes

More genetics, gotta love meiosis. As most of us know, parents pass along their genetic information to offspring. Both the mother and the father donate one set of chromosomes from a pair. We have different forms of genes, called alleles, that code for the same information. In simple cases there are only two alleles per gene and organisms usually only carry two, one from each parent. However there can be many forms of the same gene in a population.

The simplest example of allele differentiation is the famous pea plant height gene. Pea plants have two alleles for height, often denoted as “T” for the tall gene and “t” for the short gene. It was found that the tall allele covers, or obscures, the short allele whenever it is present in an organism. Alleles such as this are referred to as dominate. The short allele is only expressed when a tall allele is not present. These alleles are called recessive.

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Gregor Mendel conducted experiments with pea plants to determine this information. He created purebred plants by crossing pea plants with the tall trait many times through many generations to weed out the short alleles. He did the same process with plants that were short as he did not know the short alleles were recessive. After this he crossed pure plants with each trait.

Pea plants with two alleles for the dominate trait, TT, are called homozygous dominate and those with two recessive, tt, are called homozygous recessive. When these plants are crossed they produce offspring with Tt alleles, known as heterozygous. When two heterozygous pea plants were crossed it was found that three-fourths of the offspring were tall and one-fourth were short.

Different alleles are passed on from parent to offspring. However, there are conditions that affect the outcomes of crosses.

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Colorblindness

In humans you have to have at least one functioning color sight allele to have normal vision. The colorblindness gene is a sex linked gene, meaning it is carried on the sex chromosomes. In this case, specifically on the X. Females have two X chromosomes and males have an X and a Y. This makes males more susceptible to colorblindness. If a mother only has one good color gene, then there is a fifty-fifty shot that her son will have colorblindness.

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If a female has the gene for colorblindness it does not necessarily mean she will be colorblind. The colorblindness gene is recessive so if she has a good X without the gene, her vision will be perfectly normal. If a female is heterozygous for a sex linked gene, she is known as a carrier.

There’s the downside for males. They only have one X. So if they get a screwed up color gene, they’re going to have screwed up vision. It is not impossible for women to inherit the abnormality but it is much less common than occurrence among men.

Colorblindness has a range of severity. Cones in the eyes perceive colors. The genes in the cones contain instructions for creating different protein pigments. These pigments allow colors to be absorbed and interpreted by the brain. A variation in these genes can create different pigments, causing colors to be absorbed in an altered way.

You should see a 2 in the circle.
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Interestingly, the human eye has three color absorbing pigments in different cones. The L-cone contains pigments that absorb long wavelength light, yellows and reds. The M-cone detects midrange wavelengths, greens, and the S-cone has pigments that absorb blues.

Despite what some people think, many people who are colorblind don’t see in grey-scale. They can still see color, their eyes just have a difficult time differentiating between colors. I know a couple people who are colorblind and they often confuse shades of green and yellow, red and orange, and blue and purple. No matter how enjoyable it is to mess with people with colorblindness, you shouldn’t constantly ask them what color an object is.

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Injections in the Eye. It won’t hurt, I promise.

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Gene therapy is the future of medicine. Diseases like HIV and genetic disorders can be treated with gene therapy. Researchers have even cured colorblindness in monkeys.

According to Popular Science, Jay and Maureen Neitz of Washington University successfully cured the colorblindness of monkeys. Genes were artificially inserted into the retinas of the monkeys through surgery.

The two male squirrel monkeys that were treated had red-green colorblindness and had been colorblind since they were born, according to Nature.com. The procedure involved inserting the gene to correct the colorblindness into a virus. The virus was then “injected behind the retina” of the two monkeys. Using gene therapy, the monkeys gained the ability to create more color absorbing pigments. The monkeys were named Dalton and Sam.

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After the treatment, the monkeys could see color. Their ability to differentiate color was determined using a screen test. If the monkey touches the red colored dots, he was rewarded with grape juice.

However, researchers hope to find a way to enable this process using a noninvasive injection into the fluid in the eye. This is under development but scientists hope to carry out human trials in the next couple of years.

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Although colorblindness is not a seriously debilitating disease, finding ways to treat it could improve the lives of many people. According to the Washington University website, every 1 in 12 men and every 1 in 230 women is affected by colorblindness. Surprisingly as many as 1 in 4 women are carriers of the gene. This sort of treatment could eventually be used commonly in humans.

However, the effects of this therapy are not limited to people with colorblindness. Using this technology we could artificially end colorblindness. We would essentially be wiping out a genetic illness. The implications of this are incredible! With genetic therapy we could eventually end many genetic diseases and disorders.

Thanks for reading! I hope you see all the colors <3

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Want to find out if you’re colorblind? Take this test.