Therapeutic genes are delivered into any cell other than a gamete, germ cell, gametocyte, or undifferentiated stem cell in somatic cell gene therapy. Such changes solely impact the individual sick and are not passed on to descendants. The insertion of functional genes into the genomes of germ cells is used in germline gene therapy. When a germ cell is changed, the modified gene is found in all of the organism's cells. As a result, the alteration is heritable and may be handed down to future generations.
