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Essay

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During evolution duplication of a gene produces two copies. The sequence of one copy may continue to be conserved (because it remains subject to ____1_____ ____2____; the other copy is free to mutate. The latter will most likely acquire deleterious mutations and degenerate to become a ____3_____. If duplication occurs at the genome level, the ______3______ will often be located close to the parent gene. It may contain copies of the full length sequence of the parent gene (including the promoter, exons, and introns), and is known as a ____4_____ _____3______ . Sometimes, however, the duplication involves making a cDNA copy of an mRNA after which the cDNA copy integrates into a new locus that is often very distant from the parent gene. Because the cDNA copy lacks promoter sequences, it is usually not expressed and will acquire inactivating mutations and degenerates. This type of _____3____ is known as a _____5____ ___3_____ or a ____6_____. Sometimes, the cDNA copy integrates close to a promoter sequence and is expressed, and if so, on rare occasions, the expression of this gene copy becomes an asset to the cell so that it becomes subject to ____1____ ____2____ and is a conserved functional gene. Such a cDNA copy is known as a ____7____.