Phenotype How Variations Arise Within a Phenotype  Essay

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How variations arise within a phenotype?

Phenotype is the specific characteristics that are displayed by the organism. Phenotypic variation is a prerequisite for evolution due to natural selection, thus without the former, there is no latter. Qualitative traits are traits that show a difference between phenotypes like skin color, sex, and eye color. However, such descriptions are controlled by a small number of genes so environmental influence on these traits is low since it involves the genetics of individuals. Quantitative traits are traits that exhibit a continuous range from one phenotype to another. Therefore, there is no difference between phenotypes and are usually influenced by several gene pairs while the environment has a significant influence on the trait. This type of trait involves the genetics of populations. It is a combination of genetic and environmental factors to produce phenotypes that blend into each other. Phenotypic variance or VP is the variance of the phenotype, including physical and biochemical characteristics, which results from the sum of genetic or VG and environmental or VE variances. Thus, the equation for phenotypic variation is VP = VG + VE. However, it can also be a sum of the variance of genotypic and environmental together, thus producing VGxE. Genetic variance can be subdivided into VADD, VDOM, and VEPI. The first is phenotypic variation due to additive effects of alleles. The second is phenotypic variation due to dominance effects, which is when the effects of the allele is dependent on the identity of the other allele at the locus. The third is phenotypic variation due to epistatic effects, which is when the effect of the allele depends on the identity of alleles at different loci. According to the Stanford Encyclopedia of Philosophy (2004), it was cited that "small variations in phenotype arise in part because the interconnections of metabolic pathways in the organism are so complex that variation in proteins that are not directly part of the melanin production pathway may nevertheless have an effect on the rate of melanin formation. But these variations in such peripheral proteins are, in turn, the result of genetic variations in the genes that code for them" (p. 6). Furthermore, phenotypic variation in some traits is due to genetic differences among individuals called heritability. Heritability is the proportion of variation in trait that can respond to selection, which can be broad-sense or narrow-sense heritability. The former includes dominance and epistatic variation while the latter is the proportion of phenotypic variance that is due to additive genetic causes. However, high heritability doesn't necessarily mean the environment isn't a factor and low heritability doesn't mean genetics doesn't play a part in phenotypic variation.

2. How meiosis produces a random mix of parental genetic material in the gametes?

Meiosis is the process where germ cells produce eggs or sperm, and there is an exchange of genetic material between paired chromosomes called crossing-over. In meiosis, each gamete known as sperm or egg receives only one of each of the paired chromosomes. However, when one of the two chromosomes in each pair goes to an individual gamete, it is random, and not related to which one of the two chromosomes in any of the other twenty-two pairs goes to that gamete. This is called random assortment, and with crossing-over,…

Sources Used in Document:


Bellevue College Science Division (2011) Mutation and Genetic Diseases, [online] Available at: [Accessed: 20 April 2011].

Biology 346-Evolution (2011) Chapter 13-Evolution of Phenotypic Traits, [online] Available at: [Accessed: 20 April 2011].

Chicago Center for Jewish Genetic Disorders (2008) Intro to Genetics, [online] Available at: [Accessed: 20 April 2011].

Grimmel College (2011) Lab 2 -- Sources of Phenotypic Variation, [online] Available at: [Accessed: 20 April 2011].

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