Some forms of mutations are [[Heredity|hereditary]] ([[germline mutation]]s), or passed on from a parent to its offspring.<ref name=":4">What is a gene mutation and how do mutations occur? - Genetics Home Reference - NIH. (n.d.). Retrieved from https://ghr.nlm.nihmedlineplus.gov/primergenetics/understanding/mutationsanddisorders/genemutation/ .</ref> Such mutated coding regions are present in all cells within the organism. Other forms of mutations are acquired ([[somatic mutation]]s) during an organism's lifetime, and may not be constant cell-to-cell.<ref name=":4" /> These changes can be caused by [[mutagen]]s, [[carcinogen]]s, or other environmental agents (ex. [[Ultraviolet|UV]]). Acquired mutations can also be a result of copy-errors during [[DNA replication]] and are not passed down to offspring. Changes in the coding region can also be [[De novo mutation|de novo]] (new); such changes are thought to occur shortly after [[Fertilisation|fertilization]], resulting in a mutation present in the offspring's DNA while being absent in both the sperm and egg cells.<ref name=":4" />
