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About Mutations

A mutation is a heritable change in the genetic material of an individual. The change can be large or small. Large changes involve the loss, addition, duplication, or rearrangement of whole chromosomes or chromosome segments. The smallest changes, called point mutations, alter only a single base. The effect of a mutation depends on its size, location (intron or exon, etc.), and the type of cell in which the mutation occurs. This animation illustrates mutations that affect the production of brown and red pigments in fruit fly eyes.

If a mutation occurs in a germline cell, which includes both the gametes and the cells from which they are formed, then the mutation can be passed on to progeny. If, however, the mutation occurs in a somatic cell, only the original individual will be affected.

Even though mutations are generally portrayed as harmful, particularly by science fiction movies, the fact is that DNA repair enzymes, which are constantly scanning DNA to detect and replace any 'damaged' nucleotides, correct the vast majority of mutations. Also, many mutations have no effect on gene function at all. Finally, a small number of mutations are actually beneficial to an organism, providing a new or improved gene activity. In fact, mutations are ultimately the source of all of the genetic variation necessary for evolution.


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