What is a duplication, and what evolutionary significance might it have?

A duplication occurs when a gene or group of genes is copied to multiple regions of chromosomes. This has evolutionary significance because a gene can be retained in the original site and duplicate sites can undergo mutations that may be selected for by nature. If the mutations are advantageous, they will be passed on to further generations of the species. If the mutations are not advantageous, the original gene is still present, so no genetic information has been lost.