Essay on Genetic Variation

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Genetic Variation

Species refers to a population of organisms which are potentially capable of interbreeding to produce fertile offspring. Variation can be shown within a species. Variation is the difference between individuals within a species. Variation can be caused by genetic factors, environmental factors or a combination of both. Environmental factors which affect variation include nutrition, climate and pollution. Organisms that reproduce sexually display genetic variation. Genetic variation is a result of meiosis. Meiosis allows the independent assortment of chromosomes which contributes to variation.. Independent assortment happens at metaphase I, when the bivalents line up on the
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Each gamete has a unique combination of genes. Any of the numerous male gametes can fertilise any of the numerous female gametes, therefore every zygote is unique. In mitosis (a-sexual reproduction) the only source of variation is mutation. If a mutation occurs in a germ line it will be inherited by the offspring.

The members of a population share the same gene pool and their genes occur within particular frequencies. Natural Selection and isolation can result in changes in the allele and phenotype frequency which leads to the formation of a new species. Natural selection is when those organisms which appear physically and physiologically better adapted to their environment survive and pass on their advantageous genes to the next generation. This can lead to changes in allele frequency because only the frequencies of the better adapted are sustained.

Speciation can be caused by isolation. There are two types of reproductive isolation prezygotic isolating mechanisms and postzygotic isolating mechanisms. Examples of prezygotic isolation include ecological isolation, temporal isolation and behavioral isolation. Species occupy different habitats and so can be ecologically isolated from each other. The lion and tiger both lived in India until 150 years ago, but the lion lived in grassland and the tiger lived in forest. Consequently the two species did not interbreed

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