Color of the Eyes

The human eyes have captivating shades of colors that fluctuate depending on the race of the person. The amount of melanin in the iris and the collagen fibers in the eyes mix to give the different colours of colors such as blue, black, and green. The brown color of the eye is the most common, observed by blue, grey, and lastly green. The colorings are varying depending on the geographical vicinity as well as the race of the individual. For example, the Europeans are blue-eyed while the Africans are black or brown eyed due to the fact of the high amounts of melanin synthesized in the body. For a lengthy time, people thought that eye shade inheritance followed the simple Mendelian rule; however, scientists have established that eye color is a polygenic trait (White & Rabago-Smith, 2014). This means that multiple genes interact with one another to produce the color. Sixteen known genes are responsible for eye color. This paper will provide the evidence of the evolutionary history of the eye color inheritance.The distribution of melanin pigment is responsible for iris color. For example, the brown eye shade means that the melanin content is very high while blue color is indicative of little melanin. Geneticists have tried to model and explain the inheritance of eye color since the 19th century. They wanted to dispute the fact that eye color followed the Mendelian inheritance. Therefore in the 1980s, chromosome mapping techniques were developed, and these enabled the researchers in genetics to identify particular loci within the chromosome that were associated with the inheritance of the trait. They identified a locus named Gey on chromosome 19, and it was related to green color. Another locus designated as Bey was identified on chromosome 15 and it was responsible for brown and blue eye color. The loci contained the genes coding for the particular shade of color. Many geneticists have established that the Gey is dominant while the Bey is recessive. The Bey locus has a gene known as OCA2 that codes for a protein that stimulates the melanin-producing cells of the eyes. When the protein stimulates the cells, they produce melanin pigment that combines with collagen fibers in the iris to form the eye color (Sturm, Duffy, Zhao, & Leite, 2008). Recent research has established that OCA2 gene is a significant determinant of iris color with a 74 percent variation in the human eye. However, there are many variants of this gene with many differing by a few changes in the DNA sequence. Moreover, a study done in 2006 concluded that the variations in OCA2 genes are highly diagnostic for a particular color and that the iris shade can be predicted from the individual’s genotype of OCA2 (Sturm & Larsson, 2009). Furthermore, more new genes associated with eye color have been discovered due to the availability of the new technology of human genome sequencing. On the contrary, more research is needed to identify how these genes interact with OCA2 to bring the variations. Another gene that affects the eye color is the HERC2. It is also located on the human chromosome 15. The gene works together with OCA2 to bring about eye color inheritance. For example, the OCA2 gene produces a transporter of tyrosine on the cell membrane that acts as a precursor for melanin pigment. Therefore, any gene mutation in OCA2 gene may result in albinism, a health condition that is linked to visual problems such as increased sensitivity to light. Besides, HERC2 monitors and regulates the expression of OCA2 gene. Considering the European population, there is a polymorphism in HERC2 gene, and this is responsible for the blue eye color phenotype among the whites (White & Rabago-Smith, 2014). For instance, an individual who has two copies of HERC2 genes in chromosome 15 is likely to have the blue eyes. Moreover, if the genes mutated, they are likely to have blue eyes. Eye color being an example of polygenic inheritance is influenced by sixteen different genes. The inheritance is complicated; however, it is determined by the amount of melanin component in the iris. The blue eyes o not contains melanin, and it is a common phenotype among the Europeans. The most dominant genes that influence eye color are the OCA2 and HERC2 genes. Besides, other genes responsible for eyeshades have been identified as influencing factors for skin and hair color. Understanding the eye color inheritance and the genes responsible is necessary to calculate the phenotypic and genotypic ratios (Sturm & Larsson, 2009). A person who contains all the alleles of the genes and expressed dominantly will have the black eye color. An example is in the case of Africans who have high contents f melanin. The presence of two dominant genes may give rise to brown color while one dominant gene and one recessive gene produce a green shade. Lastly, having recessive genes results in blue eye color. In this situation, the genes have mutated, or the HERC2 and OCA2 genes have been suppressed. No melanin is produced in the iris resulting in a medical condition known as albinism (Sturm, Duffy, Zhao, & Leite, 2008). References Sturm, R., & Larsson, M. (2009). Genetics of human iris colour and patterns. Pigment Cell Melanoma Response, 22(5), 544-562.Sturm, R., Duffy, D., Zhao, Z., & Leite, F. (2008). A single SNP in an evolutionary conserved region within intron 86 of the HERC2 gene determines human blue-brown eye color. American Journal of Human Genetics, 82(2), 424-431.White, D., & Rabago-Smith, M. (2014). Genotype-phenotype associations and human eye color. Journal of Human Genetics, 56(1), 5-7.