... occur more fre-quently when DNA is exposed to mutagens, includingultraviolet light, X-rays, and certain chemicals. Mostmutations are either harmful to or don’t affect the organ-ism. In rare ... thegenotype (its genes) and its environment. By environ-ment, we don’t mean the Earth, but the environmentsurrounding the cell or organism. For example, hor-mones in the mother’s body can influence the ... on the cellular level is called mito-sis. It requires only one parent cell, which, after exactlymultiplying its genetic material, splits in two. The result-ing cells are genetically identical...