In order for a cellular change to be inherited, this change must be present in the male gamete, or sperm or present in the female gamete, the egg or ovum. This is due to the fact that a baby is created from the fusion of an egg and sperm. Therefore, choice 2, the deletion of a single DNA base in a sperm cell of a trout, is the correct answer.
If we think about it logically, cellular changes in other parts of body should not affect the next generation. For example, if mom has skin cancer, it does not mean at all that the baby will have it as well.