Difference between revisions of "Mutation"

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In biology mutation is any physical change in the genetic material of an organism. In most cases this is either the DNA or RNA in the cell nucleus. In multicellular organisms there are two primary classes of mutation, germline mutations and somatic mutations. Germline mutations are those changes that can be passed down to offspring, while somatic mutations are mutations that only alter genetic material in the mutated organism. There is some evidence that changes outside of the cell's genetic material, such as the cytoplasm, proteins, or the cell membrane can also be inherited.

Mutations can be caused by internal or external factors. Common external factors include ultraviolet radiation, chemical mutagens, or parasitic organisms (such as viruses or bacteria). Most internal causes of mutations stem from errors in reproduction of genetic material. Most of these errors are corrected by error-correcting ribosomes.

Some organisms will respond to harsh environments by increasing the rate of mutations. This is known as hypermutation and is hypothesized to aid organisms by creating wider variation in the gene pool of the population, increasing the chances that at least some decedents might survive under harsh conditions.

Types of Mutations

Morphological mutants affect the outward appearance of an individual. Plant height mutations could changes a tall plant to a short one, or from having smooth to round seeds. Biochemical mutations have a lesion in one specific step of an enzymatic pathway. For bacteria, biochemical mutants need to be grown on a media supplemented with a specific nutrient. Such mutants are called auxotrophs. Often though, morphological mutants are the direct result of a mutation in a biochemical pathway. In humans, albinism is the result of a mutation in the pathway from converts the amino acid tyrosine to the skin pigment melanin. Similarly, cretinism results when the tyrosine to thyroxine pathway is mutated. Therefore, in a strict genetic sense, if appropriate experiments are performed, a morphological mutation can be explained at the biochemical level.

For some mutations to be expressed, the individual needs to be placed in a specific environment. This is called the restrictive condition. But if the individual grow in any other environment (permissive condition), the wild type phenotype is expressed. These are called conditional mutations. Mutations that only expressed at a specific temperature (temperature sensitive mutants), usually elevated, can be considered to be conditional mutations.

Lethal mutations are mutations that lead to the death of the individual. Death does not have to occur immediately, it may take several months or even years. But if the expected longevity of an individual is significantly reduced, the mutation is considered a lethal mutation.

Wild type alleles typically encode a product necessary for a specific biological function. If a mutation occurs in that allele, the function for which it encodes is also lost. The general term for these mutations is loss-of-function mutations. The degree to which the function is lost can vary. If the function is entirely lost, the mutation is called a null mutation. If is also possible that some function may remain, but not at the level of the wild type allele. These are called leaky mutations.

Loss of function mutations are typically recessive. When a heterozygote consists of the wild-type allele and the loss-of-function allele, the level of expression of the wild type allele is often sufficient to produce the wild type phenotype. Genetically this would define the loss-of-function mutation as recessive. Alternatively, the wild type allele may not compensate for the loss-of-function allele. In those cases, the phenotype of the heterozygote will be equal to that of the loss-of-function mutant, and the mutant allele will act as a dominant.

Gain-of-function mutations create a new allele that is associated with a new function. Any heterozygote containing the new allele along with the original wild type allele will express the new allele. Genetically this will define the mutation as a dominant. A primary example of this is the sickle hemoglobin, where the function of the hemoglobin has changed in a way to be not conducive to malaria parasites. The creation science organization Answers in Genesis states the following regarding the mutation that results in sickle cell anemia:

Mutatations and the Theory of Evolution

Pierre Grasse

Evolutionist Theodosius Dobzhansky wrote: "The process of mutation is the only known source of the new materials of genetic variability, and hence of evolution."^[2] Most evolutionists believe that the processes of mutation, genetic drift and natural selection created every species of life that we see on earth today after life first came about on earth.^[3] However, Pierre Grasse, who served as Chair of Evolution at Sorbonne University for thirty years and was ex-president of the French Academy of Sciences, stated the following: "Some contemporary biologists, as soon as they observe a mutation, talk about evolution. They are implicitly supporting the following syllogism: mutations are the only evolutionary variations, all living beings undergo mutations, therefore all living beings evolve....No matter how numerous they may be, mutations do not produce any kind of evolution." Grasse pointed out that bacteria which are the subject of study of many geneticists and molecular biologists are organisms which produce the most mutants.^[4] Grasse then points that bacteria are considered to have "stabilized a billion years ago!".^[5] Grasse regards the "unceasing mutations" to be "merely hereditary fluctuations around a median position; a swing to the right, a swing to the left, but no final evolutionary effect."^[6] In addition, Harvard biologist Ernst Mayr wrote: "It must be admitted, however, that it is a considerable strain on one’s credulity to assume that finely balanced systems such as certain sense organs (the eye of vertebrates, or the bird’s feather) could be improved by random mutations."^[7]

Creationist scientists believe that mutations, natural selection, and genetic drift would not cause macroevolution.^{[8][9][10][11][12]}

References

Other References

Biology (7th Edition). Neil A. Campbell,Jane B. Reece. http://www.amazon.com/Biology-7th-Neil-Campbell/dp/080537146X.