Colorblind Case

The growth of diseases and disorders has become a prevalent topic throughout the history of mankind. A common example of these maladies is the issue of colorblindness. According to the Merriam-Webster dictionary, colorblindness is defined as being "affected with partial or total inability to distinguish one or more chromatic colors" (Merriam-Webster, Inc., 2012). This genetic trait affects the lives of many living within the world today.

"Color deficiency" (A.D.A.M., 2011), known for short as color blindness, is generally classified mainly as a sex-linked genetic disorder. Genetic diseases as a whole are usually considered incurable disorders that are linked to the DNA make-up of the individual. They are created due to a malfunction of the forming of the genetic code such as, not correctly copying the complimentary combination of DNA genetic material during replication and transcription, and failing to accurately completing the process of creating RNA during translation. Outside of DNA and RNA production, genetic disorders can be formed by other methods including adding or subtracting the number of chromosomes from the required amount in each cell; humans need forty-six chromosomes to function at optimal standards. In most cases, children receive these traits from the inheriting of their parents. These accidental changes can seem minuscule or diminutive to the naked eye, but from a molecular point of reference even the slightest change in genetic make-up can cause a devastating impact on the livelihood of the individual (Campbell, Williamson, & Heyden, 2006).

However colorblindness, specifically red-green colorblindness, is sex-linked by the occurrence of dominant and recessive sex-linked alleles. "Sex-linked alleles are those located on one sex chromosome but not the other" (Campbell, Williamson, & Heyden, 2006). The pedigree in figure 1 illustrates how two parents that are neither fully affected can give birth to an affected son. In order for this event to take place, the mother would have had to be a carrier of the disorder. This is possible because colorblindness is "X-linked recessive," meaning that the allele for this disorder is only found on the X-chromosome, but the symptoms are hidden due to a dominant allele on another X-chromosome. Since human male only have one X-chromosome, colorblindness is common for this gender. The typical transfer of colorblindness is from a mother carrying the disorder to her son, which will then affect the son. Fortunately not all children of a carrier mother are affected. According to the diagram, the parents only have about a twenty-five percent chance a fully affected son under the given conditions. The unaffected X-chromosome from the mother can combine with either unaffected chromosomes from the father, and the result will be an unaffected offspring (U.S. National Library of Medicine).

Within a normally functioning eye, there are three cone cells that correspond with obtaining an individual color - red, green, or blue - designated for the particular cell. Color blind people are usually missing or subject to a malfunction of at least one of these cone cells. Figures 2 and 3 give diagrams of the human eye to accompany the placement of cone cells. Unlike all genetic disorders, colorblindness can be caused by both genetically and physically changing the cells. By genetics, this disease is gained by inheriting it from a parent (Campbell, Williamson, & Heyden, 2006). During the majority of these genetic instances, a cone cell is just not functioning properly, opposed to not having the cell at all. However this trait can also be obtained after birth with non-parent related causes such as, "aging; eye problems, such as glaucoma, macular degeneration, cataracts, or diabetic retinopathy; injury to the eye; and side effects of some medicines" (WebMD, 2007). These factors make colorblindness different from other types of genetic diseases.

Compared to the ancient origins of other diseases, the history of color blindness is relatively short. "The first case of colorblindness was described in the late 18th century by chemist John Dalton [shown in figure 4], who was himself [color] blind. Dalton is more commonly known for developing the atomic theory, but the first paper he ever wrote described colorblindness in himself and his brother. His research started ... on this condition in the scientific community, and today, some call colorblindness Daltonism in honor of his first description" (Boyer, 2012). This new discovery led many notable scientists around the world to dig deeper in their research of the causes, results, and severity of this disorder.

As a result of these scientists' research, a series of symptoms are linked with color vision deficiency. Depending on the severity of the make-up, a varying scale of symptoms may occur. In most cases, the subject is able to see some colors but cannot discern the difference between others, such as red and green; other cases report of people seeing wrong colors, such as mistaking purple for orange and the other way around. Figure 5 compares the visibility of a typical traffic light from the point of view of a normal human and one diagnosed with red-green colorblindness (Live, 2011). In very extreme events, individuals may not be able to see any color at all, and just see the grayscale. Some animal scientists believe that other species, including canines, are given this disorder of viewing a "black and white world" (A.D.A.M., 2011). Although these symptoms are not necessarily painful, they cause some difficulties. As a child, the ability to learn and read is greatly hindered which causes a great challenge for both the student