Gene mutation is a change in DNA sequence that can make a gene different from the original one permanently. Gene mutation can happen in two ways. The first way is that the mutation occurs during lifetime (after being born). This kind of mutation is more related to environment changes, like exposure to strong alpha radiation in a lab by accident, or exposure to strong ultraviolet ray from the sun very often.Sometimes it it not due to environment problems, but the mistakes occur during DNA replication process. DNA replication is like the copy machine making copies. It is possible that there are errors when so many replication processes are going on. The second way is that the mutation comes from parent. In other words, the mutation is inherited from parent, and that is called hereditary mutation. This kind of mutation starts in the spern and egg cells, so they will exist in every cell of the body. When talking about mutation, no cells can be regarded as normal forever. Why? Because sometimes the same kind of mutation happens so often in many many individuals that the number of individuals that have this mutation is more than those who don’t have mutations, so the mutants are therefore called the “normal” ones. Sometimes mutations are good, sometimes they are bad. The good mutations that are inheritable will be passed on the the next generations, while the bad ones are not likely to be passed on, since those bad mutations have more disadvantages when competing with the others. Remember Darwin said “survival the fittest”?