A chromosomal mutation known as duplication is more commonly associated with the genes that have information for the formation of the following in many a organism. 

A cell organism requires the formation of more ribosomes than any other cell organelle as more proteins have to be synthesized with its involvement. Hence in most of the organisms there are several copies of ribosomal DNA in the same chromosome or different chromosomes a set of chromosomes. Gene duplication takes place during meiosis due to irregular crossing over.