Life originated from a common ancestor and due to various mechanisms of evolution, the genotype of organisms has changed. Mutation, migration, genetic drift and selection are natural processes of evolution that affect genetic diversity. Mutations are spontaneous changes in genomic sequences (Robert, et al., 2006); it is one of the processes that influence allele frequency. A mutation can either have a positive, negative or a neutral effect on an organism’s fitness. When organisms of the same species exhibit different phenotypes, the organism is polymorphic for that particular trait. A beneficial mutation that gives rise to polymorphic traits can improve the chance of survival. For example, the grove snail, Cepaea nemoralis, is famous for the rich polymorphism of its shell. A mutation in the locus responsible for colour produces different shell colours, ranging from yellow, pink, white and brown (Ozgo, 2005). Snails with brown shells are found in beechwoods where the soil is dark. Snails with brown shells are able to camouflage with the soil, thus avoiding being detected by predators (Jones, et al, 1977). As a result of avoiding predation, the frequency of alleles that code for brown shells will increase. However, according to the hitchhiking model, fixation of a beneficial mutation will decrease the diversity at linked loci (Chevin, et al., 2008). If a new mutation increases the fitness of members of a particular species, a strong selective sweep on allele frequency will result to very few haplotypes existing in the population. The frequency of alleles that are positively selected and those that are closely linked will increase, but the other alleles will decrease.
A mutation can be neutral, having neither a beneficial effect nor a negative effect. However, some mutations are lethal because they have a negative effect on fitness. The accumulation of deleterious mutations and... [continues]
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