The variation that selection requires arises from two distinct sources. The ultimate sources of variation are gene mutation, gene duplication and disruption, and chromosome rearrangements. Gene mutations are randomly occurring events that at a molecular level consist mostly of substitutions or small losses or gains of nucleotides within genes. Gene duplication makes new copies of existing genes, while gene disruptions destroy functional copies of genes, often through insertion of a mobile genetic element. Chromosome genotype set of genes present mutation change in DNA sequence

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