The University of Illinois at Chicago explains that DNA must replicate itself so that during cell division, both daughter cells receive the same genetic information. DNA replication is necessary during the process by which somatic cells divide, called mitosis, as well as during meiosis, the process by which organisms produce gametes, or sex cells.
The goals of mitosis and meiosis are different, which necessitates the difference in the process of cell division. As stated by the University of Illinois at Chicago, body cells require the organism’s full complement of chromosomes, while gametes only receive one chromosome from each pair. This is because upon meeting the complimentary sex cell, each gamete contributes one copy of each chromosome, yielding an organism with a unique genome. By contrast, body cells do not produce new genomes; they perform basic life functions or comprise the body’s structures.
DNA replication is a complex event that is controlled by several different enzymes. According to Wikipedia, one such enzyme is DNA polymerase. During the process of replicating DNA, DNA polymerase occasionally makes an error. While most of these errors have little or no effect on an organism, some can have drastic results. Fortunately, such mistakes are rare, only occurring about once in every billion base pairs.