Chromosome duplication: Part of a chromosome in duplicate. A particular kind of mutation involving the production of one or more copies of any piece of DNA, including sometimes a gene or even an entire chromosome.
A duplication is the opposite of a deletion.
Duplications have been important in the evolution of the human genome (and the genomes of many other organisms). Duplications typically arise from an event termed unequal crossing-over (recombination) that occurs between misaligned homologous chromosomes during meiosis (germ cell formation). The chance of this event happening is a function of the degree of sharing of repetitive elements between two chromosomes. The recombination products of such an event are a duplication at the site of the exchange and a reciprocal deletion. A remarkable class of duplications in which the duplicated region has popped up far away from home base has also been discovered.