Sometimes, individual [[Gene]]s, pieces of [[Chromosome]]s, entire [[Chromosome]]s, or entire [[Genome]]s can be duplicated.
Once a Gene is duplicated, there are three possible pathways:
 1. Both copies may remain functional and continue to produce identical Gene products. NaturalSelection favors multiple copies of a Gene when large amounts of the Gene product are required. 
 1. One copy of the gene can retain its original function and the other can accumulate mutations, degenerate, and ultimately become nonfunctional.
 1. The most interesting from an evolutionary point of view : One copy of a newly duplicated gene may maintain its original function, and the other may evolve to acquire a new function.

E.g. [[Globin]] gene

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AnswerMe : In case 1, do these two genes have same name or different name? --[[yong27]], 2004-10-09