Mutation develop best adaptations or harms. Review on Mutation - Robin Cook

Mutation is actually a change in tiny part of DNA, there may be different agents that cause mutation in organisms may be plants or animals.so here many question arises,

what are the types of mutation, how mutation occur, why mutation occur, which agents cause mutation, and finally what are the effects of mutation, either mutation in each and every part of world occur or it causes and intensity may occur at any point in the world, sources of mutation may be the sources of rays or cosmic rays or any harmful toxic material like chemical may cause mutation, mutation change the sequence of triplet code or codon which ultimately leads to harmful effects like in pancreas specific genetic code specify to produce insulin but single gene change may introduce to inhibit the proper and normal functioning of the pancreas so in that sense it looks harmful.