Cancer is basically a condition involving the control of tissue growth. Changes in the genes that control cell development and differentiation are required for a normal cell to develop into a cancer cell. Genetic alterations can take place on a variety of scales, from the addition or deletion of entire chromosomes to a mutation impacting a single DNA nucleotide. There are many different classification systems for the numerous genetic alterations that could lead to the development of cancer cells. Mutations, or changes in the nucleotide sequence of genomic DNA, account for the majority of these alterations. An aberrant number of chromosomes, or aneuploidy, is a genetic change that does not entail a mutation. It might involve the gain or loss of one or more chromosomes due to mistakes in mitosis.