Editing Germline mutation (section)

== When mutagenesis occurs ==
Germline mutations can occur before fertilization and during various stages of zygote development.<ref name=":0" /> When the mutation arises will determine the effect it has on offspring. If the mutation arises in either the sperm or the oocyte before development, then the mutation will be present in every cell in the individual's body.<ref name=":9">{{cite journal | vauthors = Samuels ME, Friedman JM | title = Genetic mosaics and the germ line lineage | journal = Genes | volume = 6 | issue = 2 | pages = 216–37 | date = April 2015 | pmid = 25898403 | doi = 10.3390/genes6020216 | pmc=4488662| doi-access = free }}</ref> A mutation that arises soon after fertilization, but before germline and somatic cells are determined, then the mutation will be present in a large proportion of the individual's cell with no bias towards germline or somatic cells, this is also called a gonosomal mutation.<ref name=":9" /> A mutation that arises later in zygote development will be present in a small subset of either somatic or germline cells, but not both.<ref name=":0" /><ref name=":9" />