Mutations on somatic cells cannot be passed down to offspring. Rather mutations born on gametic cells are what can be passed down. This is because gametes are the cells involved in fertilization to form zygote that develops into individual organisms.
Explanation:
Mutation on gametic cells can occur within the time from the pre-gametic cell to the formation of a mature gamete such as sperm or egg.
Radiation from nuclear reactor accidents in Japan in April 2011, may damage the cell of the body both somatic and gametic. But only those in the gametic cells are passed down Children born to these Japanese people. Radiation causes double-stranded breaks in DNA that are hard to repair by repair mechanisms in the cell leading to mutations.
