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Pseudogenes are DNA sequences that resemble genes but are not correctly transcribed or translated to a functional polypeptide. If a functional gene is duplicated so that there are two nonhomologous copies of it in the genome, one of the copies can retain the code for the original polypeptide product, while the other is free from such constraints, since one copy of the gene is sufficient to produce the protein. Because mutations in one copy do not destroy the gene’s function, they may be retained, and the unneeded copy can evolve more quickly. It may change to produce a different, functional polypeptide (and effectively become a new gene), or it may remain nonfunctional as a pseudogene. There are two types of pseudogenes, defined by how they were produced: nonprocessed and processed.