Mutation
 

[SIZE="4"][COLOR="Magenta"]Mutation[/COLOR][/SIZE]

Mutations are changes to the base pair sequence of genetic material (either DNA or RNA). Mutations can be caused by copying errors in the genetic material during cell division and by exposure to ultraviolet or ionizing radiation, chemical mutagens, or viruses, or can occur deliberately under cellular control during processes such as meiosis or hypermutation.

Mutations create variation in the gene pool, and the less favorable (or deleterious) mutations are removed from the gene pool by natural selection, while more favorable (beneficial or advantageous) ones tend to accumulate, resulting in evolutionary change. For example, a butterfly may develop offspring with a new mutation caused say by ultraviolet light from the sun. In most cases, this mutation is not good, since obviously there was no 'purpose' for such change at the molecular level. However, sometimes a mutation may change, say, the butterfly's color, making it harder for predators to see it; this is an advantage and the chances of this butterfly surviving and producing its own offspring are a little better, and over time the number of butterflies with this mutation may form a large percentage of the species.

[SIZE="4"][COLOR="Magenta"]Harmful mutations[/COLOR][/SIZE]

Changes in DNA caused by mutation can cause errors in protein sequence, creating partially or completely non-functional proteins. To function correctly, each cell depends on thousands of proteins to function in the right places at the right times. When a mutation alters a protein that plays a critical role in the body, a medical condition can result. A condition caused by mutations in one or more genes is called a genetic disorder. However, only a small percentage of mutations cause genetic disorders; most have no impact on health. For example, some mutations alter a gene's DNA base sequence but don’t change the function of the protein made by the gene.

If a mutation is present in a germ cell, it can give rise to offspring that carries the mutation in all of its cells. This is the case in hereditary diseases. On the other hand, a mutation can occur in a somatic cell of an organism. Such mutations will be present in all descendants of this cell, and certain mutations can cause the cell to become malignant, and thus cause cancer.

Often, gene mutations that could cause a genetic disorder are repaired by the DNA repair system of the cell. Each cell has a number of pathways through which enzymes recognize and repair mistakes in DNA. Because DNA can be damaged or mutated in many ways, the process of DNA repair is an important way in which the body protects itself from disease.


[SIZE="4"][COLOR="magenta"]Beneficial mutations[/COLOR][/SIZE]

A very small percentage of all mutations actually have a positive effect. These mutations lead to new versions of proteins that help an organism and its future generations better adapt to changes in their environment. For example, a specific 32 base pair deletion in human CCR5 (CCR5-32) confers HIV resistance to homozygotes and delays AIDS onset in heterozygotes.The CCR5 mutation is more common in those of European descent. One theory for the etiology of the relatively high frequency of CCR5-32 in the European population is that it conferred resistance to the bubonic plague in mid-14th century Europe.




Source :wilkepedia