 If only a single copy of a gene existed in the genome of a species, the proteins transcribed from this gene would be essential to their survival.Because there was only a single copy of the gene, they could not undergo mutations which would potentially result in new genes; however, gene duplication allows essential genes to undergo mutations in the duplicated copy, which would ultimately give rise to new genes over the course of evolution.Mutations in the duplicated copy were tolerated because the original copy contained genetic information for the essential gene's function.