Somatic mutation

If a mutation occurs after fertilisation of an egg, not all tissues of the developing individual are usually affected by this mutation. By definition, the cells of the germline (see also germline mutation) are not affected by the mutation.

A special form is represented by immediate postzygotic mutations, which occur in the zygote or the first division stages. These mutations are distributed only to certain germ layers and thus cause the emergence of a genetic mosaic.