mutation

a change that takes place in the DNA (the genetic material) of the CHROMOSOMES of a cell, which is normally a rare event. The change may involve the structure or number of whole chromosomes or take place at one GENE site. Mutations are caused by faulty replication of the cell's genetic material at cell division. If normal body (somatic) cells are involved, there may be a growth of altered cells or a TUMOUR , or these may be attacked and destroyed by the IMMUNE system. In any event, this type of mutation cannot be passed on. If the sex cells (ova or sperm) are involved in the mutation, the alteration may be passed on to the offspring, producing a changed characteristic.