Mutation And Evolution
Mutation conjures up images of a sudden and dramatic alteration in appearance, behavior, or some other characteristic of living organisms. Indeed, this aspect was the basis of the term mutation when it was coined in 1901 by Dutch botanist Hugo De Vries. But, the term mutation also refers to the inheritance of an altered gene, even through multiple generations.
Every human genetic trait is subject to mutation. Indeed, some mutations—like hairless skin—must have occurred long ago because they are shared by all humans. Other traits occur only in certain populations of people. Cystic fibrosis, for instance, is most common in people of northern European descent. Sickle cell anemia, a serious blood disease, occurs frequently in people of African and Mediterranean ancestry. Tay-Sachs disease, a fatal disorder, is found primarily in Jews with eastern European ancestors. This suggests that the first person in whom such a mutation occurred came from that particular ethnic group. It may be that not enough time has lapsed, evolutionarily, to allow the mutation to spread to the wider population. Or, it can also be true that a mutation confers a selective advantage on a certain group of people. An example of the latter point is sickle cell anemia, which, in native Africans, can be protective against malaria.
Over millions of years, advantageous mutations have allowed life to develop and diversify from primitive cells into the multitude of species on Earth today, including Homo sapiens. Indeed, the appearance of a mutation, the "testing" of that mutation, and the subsequent inheritance or noninheritance of the mutation is the driving force of evolution. If DNA always replicated perfectly and with no change, every life form from bacteria to humans would have remained unchanged for the entire time of their existence on Earth. Since the planet has and continues to experience change, the inability to adapt to the changes would doom a species to extinction.
Mutations have been exploited by man for commercial purposes. Animal and plant breeders use mutations to produce new or improved species of crops and livestock. Careful breeding in this manner has spawned all the different species of dogs and horses we know today. It has resulted in crops that are resistant to drought or insecta and whose yield is improved. Controlled mutation and breeding has produced goldfish, yellow roses, and Concord grapes.
The processes that generate mutations are collectively termed mutagenesis. In the laboratory, mutagenesis can be accomplished in a controlled and precise manner. This genetic technique is called insertional mutagenesis. It is used to selectively disable genes, in order to find out what functional significance the gene product has to the cell. The ability of microbiologists to introduce controlled and precise mutations in the genetic material of bacteria and viruses can increase the understanding of the operation of the organisms, and of the mechanisms they use to cause disease. Other uses of the technique include the study of gene expression and the study of how a protein's three-dimensional structure influences its function.
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