A mutation is a change in the DNA of an organism. More specifically mutations are changes to the nucleotide sequence of the genetic material of an organism usually occurring because of errors in replication or repair.
Mutations may also be caused by exposure to ultraviolet or ionizing radiation, chemical mutagens, or viruses, or can be induced by the organism itself, by cellular processes such as hypermutation.
Types of Mutations
Not all mutations serve evolution. Somatic cell mutations occur in the DNA of somatic (body) cells and can’t be passed on to offspring in animals but can be passed on in plants through asexual reproduction. Somatic cell mutations are at work in human cancer tumors but have proven useful in the development of Navel oranges and Red Delicious apples. The mutations that matter most in evolution are germ line mutations as those mutations occur in reproductive cells – sperm or egg – and can be passed on to offspring.
Mutations are Random Events
Mutations may occur spontaneously at the molecular level in several forms or they may be induced by mutagens such as certain chemicals and solar radiation. They may be small-scale (point mutations) affecting only a few nucleotides of a single gene or large-scale affecting the structure of entire chromosomes.
Mutations may be beneficial, neutral, or harmful for the organisms but they are always totally random. Whether a mutation happens or not is unrelated to how useful or detrimental that mutation could be.
Mutation in Action
Mutations create variation within the gene pool. Less favorable (or deleterious) mutations can be reduced in frequency in the gene pool by natural selection, while more favorable (beneficial or advantageous) mutations may accumulate and result in adaptive evolutionary changes.
Imagine that in a lake a small population of bright silver-colored fish has arisen from a germ line mutation. This mutation may have proven detrimental in some situations but favorable in others. Bright colored fish in shallow water on a cloudy day would be easily seen by predators but the same fish in deeper water near the surface on a bright sunny day would very hard for predators to detect. Because the mutation was more beneficial than detrimental, natural selection has maintained the mutation in the new small but growing bright silver-colored fish population.
Evolutionists and geneticists have come to realize that mutation is the ultimate source of genetic variation. Furthermore, mutation is generally accepted by the biological community as the mechanism upon which natural selection acts, providing advantageous new traits that survive and multiply in offspring or disadvantageous traits that die out with weaker organisms.
Mechanisms of Evolution
Evolution encompasses changes on two vastly different scales – from an increase in the frequency of a gene for colored spots on the feathers of a bird (microevolution) to something as grand in scale as the evolution of the entire bird lineage (macroevolution). Despite the scale on which it happens, evolution at both levels is driven by the primary mechanisms of natural selection mutation, genetic drift, and gene flow.
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