presence of an extra segment of DNA, resulting in redundant copies of a portion
of a gene, an entire gene, or a series of genes, usually caused by unequal
crossing-over during gene replication when gametes are formed in meiosis
Definition from: GeneReviews
from the University of Washington and the National Center for Biotechnology Information
Duplication is a type of mutation that involves the production of one or more copies of a gene or region of a chromosome. Gene and chromosome duplications occur in all organisms, though they are especially prominent among plants. Gene duplication is an important mechanism by which evolution occurs.