Answer
Since prokaryotes have only one copy, the entire phenotype is determined by that one gene. Humans have two copies, which allows for greater phenotypic variation. It also provides a backup in case a certain gene is damaged by mutations. Prokaryotes do not have these features.
Work Step by Step
The question asks what the purpose of having two genes that code for the same thing is. This can be for greater variation or as a backup in case one of the copies is damaged.
