mutation

mutation


A mutation is a permanent change in the sequence of DNA. In order for an observable effect, mutations must occur in gene exons or regulatory elements. Changes in the non-coding regions of DNA (introns and junk DNA) generally do not affect function.

most mutations are neutral; they either make no change in the expression of any gene, or the changes made do not affect the function of any gene product.
1.
A large percentage of DNA is not part of any gene, and has no known function. Changes in these portions of the DNA do not alter any gene and are thus silent.
2.
Because of the wobble concept, the exact identity of the third base of a codon often makes no difference, and if it does, the two amino acids coded for by the old the the new codon are often quite similar in nature, so a change in the DNA of a gene which affects one of these bases will often have no effect on the function of the gene product. This genearlly includes 1/4-1/5 of the bases in the gene. These would be silent or neutral mutations.
3.
Not all portions of a protein are equally important for the function of that protein. Even a mutation which changes an amino acid in the final gene product may not make a difference in the function of the protein, or may alter the precise nature of the function of the gene product without alter the usefulness of that product. These would be neutral mutations.


causes mutations
Mutations can be caused by external (exogenous) or endogenous (native) factors, or they may be caused by errors in the cellular machinery. Physical or chemical agents that induce mutations in DNA are called mutagens and are said to be mutagenic.
Exogenous factors: environmental factors such as sunlight, radiation, and smoking can cause mutations.
Endogenous factors: errors during DNA replication can lead to genetic changes as can toxic by-products of cellular metabolism.