Iris Biology: The Genetics Behind Eye-Color

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The Genetics of Iris Pigmentation
This paper delves into the genetics behind eye-color. The topic of this paper was driven by an eagerness to understand the genes that are involved in the phenotypic expression of eye-color. Using the concepts of genetics and heredity one can begin to understand how traits are passed down from parents to offspring. The process is immensely complex and numerous factors can influence variability within that typical process. To begin this paper, the main concepts and definitions of genetics are explained.
The study of genetics encompasses all aspects of heritable material and its transmission. Scientists like Fredrick Griffith, Alfred Hershey, and Martha Chase were involved in the discovery that genes and DNA …show more content…
Chromosomes are located in the nucleus of a cell. They are made up of three parts: A short-arm, a long-arm, and a centromere in-between the two arms. Humans have forty-six total chromosomes and are therefore called diploid organisms. Humans receive twenty-three chromosomes from each parent. Twenty-two of those chromosomes are autosomal and one is a sex chromosome. The twenty-two autosomal chromosomes are called homologous pairs because they carry the same genes but likely in several different DNA nucleotide combinations. As mentioned earlier, alternate forms of genes are called alleles. While autosomal chromosomes occur in homologous pairs, there are two different sex chromosomes in humans that code for different male and female traits. The two different sex chromosomes are the X- and Y-chromosomes. They vary in size and are also carrying different genes on them. Generally, the presence of a Y-chromosome determines that a child will display male phenotype. The SRY gene on the Y-chromosome is responsible for triggering male differentiation during embryonic development. While human mothers can only pass on the X-chromosome, fathers can pass on an X- or a Y- chromosome. For this reason it is said that fathers determine the sex of their …show more content…
Haploid gametes have twenty-three chromosomes in their nucleus, while normal human diploid cells have 46 chromosomes in their nucleus. In meiosis, haploid gametes are produced through “two successive cell divisions” (Cummings, 2014). Gametes only become diploid after fertilization of an egg (female gamete) by a sperm cell (male gamete). Variation is very important for a species and for the individuals within that species because it increases the likelihood of survival in various environmental conditions. Humans are diploid organism and receive a combination of genes from their parents, this allows for variation, thus making the species more competitive as a whole. Other mechanisms that help to create variation among humans are found in the process of meiosis and include random fertilization, crossing over, and independent assortment. Random fertilization means that every gamete has an equal opportunity of being fertilized. Crossing over occurs in meiosis I during prophase I and it is when new combinations of genes are created between homologous chromosomes. Independent assortment occurs in metaphase I when chromosomes randomly arrange themselves independently of other chromosomes to be dividing into separate cells. These mechanisms allow for an abundance of genetic variation in each
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