Gene amplification or duplication refers to circumstances in which there are several copies of the same gene situated on one chromosome or spread across several.
The eukaryotic genome contains long repetitive sections that code for gene products that are required in large quantities.
These genes are expressed when large amounts of the gene product are needed, such as the production of histones after DNA replication and the production of rRNA during early cell development.
Gene amplification is often the result of mutations. Most duplicate genes serve no functional purpose and are lost.