Why do you take the DNA out of a somatic cell instead of taking it out of a sex cell?

Mitosis occurs in somatic cells; this means that it takes place in all types of cells that are not involved in the production of gametes. Prior to each mitotic division, a copy of every chromosome is created; thus, following division, a complete set of chromosomes is found in the nucleus of each new cell. Indeed, apart from random mutations, each successive duplicate cell will have the same genetic composition as its parent, due to the inheritance of the same chromosome set and similar biological environment. This works well for replacing damaged tissue or for growth and expansion from an embryonic state.

Because the genes contained in the duplicate chromosomes are transferred to each successive cellular generation, all mitotic progeny are genetically similar. However, there are exceptions. For example, there are genetic variations that arise in clonal species, such as bacteria, due to spontaneous mutations during mitotic division.