Mutations are permanent, sometimes transmissible (if the change is to a germ cell) changes to the genetic material (usually DNA or RNA) of a cell. Mutations can be caused by copying errors in the genetic material during cell division and by exposure to radiation, chemicals, or viruses, or can occur deliberately under cellular control during the processes such as meiosis or hypermutation. In multicellular organisms, mutations can be subdivided into germline mutations, which can be passed on to progeny and somatic mutations, which (when accidental) often lead to the malfunction or death of a cell and can cause cancer. Mutations are considered the driving force of evolution, where less favorable (or deleterious) mutations are removed from the gene pool by natural selection, while more favorable (or beneficial) ones tend to accumulate. Neutral mutations do not affect the organism's chances of survival in its natural environment and can accumulate over time, which might result in what is known as punctuated equilibrium; the modern interpretation of classic evolutionary theory. It should be noted that, contrary to science fiction, the overwhelming majority of mutations have no real effect. Gametes (in Greek: γαμέτες) —also known as sex cells, germ cells, or spores—are the specialized cells that come together during fertilization (conception) in organisms that reproduce sexually. ... Genetic material is the material used to store genetic information for a living organism. ... Space-filling model of a section of DNA molecule Deoxyribose nucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and many viruses). ... Ribonucleic acid (RNA) is a nucleic acid consisting of a string of covalently-bound nucleotides. ... Cells in culture, stained for keratin (red) and DNA (green) The cell is the structural and functional unit of all living organisms, sometimes called the building blocks of life. ... Cell division is the process of a biological cell (called a mother cell) dividing into two daughter cells. ... Radiation generally means the transmission of objects or information from a source into a surrounding medium or destination. ... A common alternate meaning of virus is computer virus. ... Overview of the major events in meiosis Meiosis (a Greek word meaning decrease) is a cellular process that forms the basis for sexual reproduction, together with syngamy. ... Hypermutation is the central aspect to making the Acquired immune system possible. ... Germline is a word used in biology and genetics. ... Somatic means to refer to the body. ... When normal cells are damaged or old they undergo apoptosis; cancer cells, however, avoid apoptosis. ... Charles Darwin, the father of evolutionary theory Although generally, evolution is taken to mean any process of change over time, in the context of life science, evolution is a change in the traits of living organisms over generations, including the emergence of new species. ... Alternative meaning Natural Selection (computer game). ... The neutral theory of molecular evolution (also, simply the neutral theory of evolution) is an influential theory that was introduced with provocative effect by Motoo Kimura in the late 1960s and early 1970s. ... Punctuated equilibrium, or punctuated equilibria, is a theory of evolution which states that changes such as speciation can occur relatively quickly, with long periods of little change—equilibria—in between. ... Science fiction is a form of speculative fiction principally dealing with the impact of imagined science and technology, or both, upon society and persons as individuals. ...

Types of mutations

Different types of mutations.

Basic types of mutations are:

• Small-scale mutations affecting one or a few nucleotides, including:
  • Point mutations, often caused by chemicals or malfunction of DNA replication, exchange a single nucleotide for another. Most common is the transition that exchanges a purine for a purine or a pyrimidine for a pyrimidine (A ↔ G, C ↔ T). A transition can be caused by nitrous acid, base mispairing, or mutagenic base analogs such as 5-bromo-2-deoxyuridine (BrdU). Less common is a transversion, which exchanges a purine for a pyrimidine or a pyrimidine for a purine (C/T ↔ A/G). A point mutation can be reversed by another point mutation, in which the nucleotide is changed back to its original state (true reversion) or by second-site reversion (a complementary mutation elsewhere that results in regained gene functionality). There are three kinds of point mutations, depending upon what the erroneous codon codes for:
    • silent mutations: codes for the same amino acid, so has no effect
    • missense mutations: codes for a different amino acid
    • nonsense mutations: codes for a stop, which can truncate the protein
  • Insertions add one or more extra nucleotides into the DNA. They are usually caused by transposable elements, or errors during replication of repeating elements (e.g. AT repeats). Most insertions in a gene can cause a shift in the reading frame (frameshift) or alter splicing of the mRNA, both of which can significantly alter the gene product. Insertions can be reverted by excision of the transposable element.
  • Deletions remove one or more nucleotides from the DNA. Like insertions, these mutations can alter the reading frame of the gene. They are irreversible.

• Large-scale mutations in chromosomal structure, including:
  • Amplifications (or gene duplications) leading to multiple copies of chromosomal regions, increasing the dosage of the genes located within them
  • Deletions of large chromosomal regions, leading to loss of the genes within those regions
  • Mutations whose effect is to juxtapose previously separate pieces of DNA, potentially bringing together separate genes to form functionally distinct fusion genes (e.g. bcr-abl). These include:
    • Chromosomal translocations: attaching DNA from separate chromosomes
    • Interstitial deletions: removing regions of DNA from a single chromosome, thereby apposing previously distant genes (e.g. fig-ros)
    • Chromosomal inversions: switching the orientation of a segment of a chromosome, thereby apposing its ends to previously distant genes
  • Loss of heterozygosity: loss of one allele, either by a deletion or recombination event, in organisms which previously had two

A point mutation is a type of mutation that causes the replacement of a single base pair with another pair. ... A nucleotide is an organic molecule consisting of a heterocyclic nucleobase (a purine or a pyrimidine), a pentose sugar (deoxyribose in DNA or ribose in RNA), and a phosphate or polyphosphate group. ... Purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring that is fused with an imidazole ring. ... Pyrimidine is a heterocyclic aromatic organic compound, which is similar to benzene and pyridine and that contains two nitrogen atoms at positions 1 and 3 of the six-membered ring. ... Nitrous acid weak monobasic acid known only in solution and in the form of nitrite salts. ... Also known as 5-bromo-2-deoxyuridine, this chemical is a base analog of thymidine, with the thymine substituted by bromouracil. ... Silent mutations or synonymous mutations are DNA mutations that, although they alter a particular codon, they do not alter the final amino acid, and hence do not affect the final protein. ... In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. ... Missense mutations or nonsynonymous mutations are types of point mutations where a nucleotide is changed which results in a different amino acid. ... In genetics, a nonsense mutation is a point mutation in a sequence of DNA that results in a premature stop codon (also called a nonsense codon) in the transcribed mRNA, and possibly a truncated (and often nonfunctional) protein product. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Transposons are sequences of DNA that can move around to different positions within the genome of a single cell, a process called Transposition. ... In biology, a reading frame is a contiguous and non-overlapping set of three-nucleotide codons in DNA or RNA. There are 3 possible reading frames in a strand. ... Framing error is the following: Generally, a framing error is the result of reading a string of symbols which are grouped in blocks starting at the wrong point. ... Ribonucleic acid (RNA) is a nucleic acid consisting of a string of covalently-bound nucleotides. ... Transposons are sequences of DNA that can move around to different positions within the genome of a single cell, a process called Transposition. ... In biology, a reading frame is a contiguous and non-overlapping set of three-nucleotide codons in DNA or RNA. There are 3 possible reading frames in a strand. ... Figure 1: Chromosome. ... Categories: Stub | Molecular genetics | Evolutionary biology ... Fusion gene - Wikipedia /**/ @import /skins/monobook/IE50Fixes. ... Chromosomal translocation of the 4th and 20th chromosome. ... An inversion is a chromosome rearrangement in which a segment of a chromosome is reversed end to end. ... Loss of heterozygosity in a cell represents the loss of a single parents contribution to part of its genome. ... An allele is any one of a number of alternative forms of the same gene occupying a given locus (position) on a chromosome. ... Recombination usually denotes a genetic event that occurs during the formation of sperm and egg cells (especially in areas of study of biology topics). ...

Causes of mutation

Two classes of mutations are spontaneous mutations (naturally occurring) and induced mutations caused by mutagens. In biology, a mutagen (Latin, literally origin of change) is an agent that changes the genetic information (usually DNA) of an organism and thus increases the number of mutations above the natural background level. ...

Spontaneous mutations on the molecular level include:

• Tautomerism
  • Keto ↔ Enol
  • Amino ↔ Imino
• Depurination ap-site (loss of A or G); occurs 1000 times each day in mammals
• Deamination base analogs (C→Uracil or A→HX); occurs 100 times each day in mammals
• Transition
• Transversion
• Frameshift mutation (insertion or deletion on one strand), usually through a polymerase error when copying repeated sequences
• Oxidative damage caused by oxygen radicals

Induced mutations on the molecular level can be caused by: Tautomers are organic compounds that are interconvertible by a chemical reaction called tautomerization. ... Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals primarily characterized by the presence of mammary... Deamination is the removal of an amine group from a molecule. ... A frameshift mutation (also called a frameshift or a framing error) is a mutation that inserts or deletes a single nucleotide from a DNA sequence. ... Categories: Biochemistry stubs | EC 2. ... General Name, Symbol, Number Oxygen, O, 8 Chemical series nonmetals Group, Period, Block 16 (VIA), 2, p Density, Hardness 1. ... Radical is derived from the Latin word radix, which means root. In various fields of endeavor, it can mean: Sciences in chemistry, either an atom or molecule with at least one unpaired electron, or a group of atoms, charged or uncharged, that act as a single entity in reaction. ...

• Chemicals
  • Nitrosoguanidine (NTG)
  • Base analogs (e.g. BrdU)
  • Simple chemicals (e.g. acids)
  • Alkylating agents (e.g. N-ethyl-N-nitrosourea (ENU))
  • Methylating agents (e.g. ethane methyl sulfonate (EMS))
  • Polycyclic hydrocarbons (e.g. benzpyrenes found in internal combustion engine exhaust)
  • DNA intercalating agents (e.g. ethidium bromide)
  • DNA crosslinker (e.g. platinum)
  • Oxygen radicals
• Radiation
  • Ultraviolet radiation
  • Ionizing radiation

DNA has so-called hotspots, where mutations occur up to 100 times more frequently than the normal mutation rate. A hotspot can be at an unusual base, e.g., 5-methylcytosine. A base analog is a chemical that can substitute a normal nucleobase in nucleic acids. ... Also known as 5-bromo-2-deoxyuridine, this chemical is a base analog of thymidine, with the thymine substituted by bromouracil. ... An acid (often represented by the generic formula AH) is typically a water-soluble, sour-tasting chemical compound. ... ENU, also known as N-ethyl-N-nitrosourea (chemical formula C3H6N3O2), is a highly potent mutagen in the mouse. ... In chemistry, a hydrocarbon is a cleaning solution consisting only of carbon (C) and hydrogen (H). ... A colorized automobile engine An internal combustion engine is an engine that is powered by the expansion of hot combustion products of fuel directly acting within an engine. ... The word exhaust can mean:- A verb meaning tire out, as in After the long gallop, his horse was exhausted. ... Ethidium bromide (EtBr) is an intercalating agent commonly used as a nucleic acid stain in molecular biology laboratories for techniques such as agarose gel electrophoresis. ... Platinum is also a certification by the RIAA and other world recording industries, see: RIAA certification General Name, Symbol, Number Platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10 , 6, d Density, Hardness 21. ... Ultraviolet (UV) radiation is electromagnetic radiation of a wavelength shorter than that of the visible region, but longer than that of soft X-rays. ... Ionizing radiation is radiation in which an individual particle (for example, a photon, electron, or helium nucleus) carries enough energy to ionize an atom or molecule (that is, to completely remove an electron from its orbit). ... A hotspot is a center of high activity within a larger area of low activity. ... 5-methylcytosine is the methylated form of cytosine. ...

Mutation rates also vary across species. Evolutionary biologists have theorized that higher mutation rates are beneficial in some situations, because they allow organisms to evolve and therefore adapt faster to their environments.

Mutation and disease

Spontaneous, induced and hereditary mutations can cause human disease. Mutation can affect human health, causing disease by disrupting a cell's normal biological functions. For the scientific journal Heredity see Heredity (journal) Heredity (the adjective is hereditary) is the transfer of characters from parent to offspring, either through their genes or through the social institution called inheritance (for example, a title of nobility is passed from individual to individual according to relevant customs and...

Changes in the DNA caused by mutation can cause errors in protein sequence, creating partially or non-functional proteins. To function correctly, each cell depends on thousands of proteins to function in the right places at the right times. Sometimes, gene mutations prevent one or more of these proteins from functioning correctly, causing malfunction or loss of a necessary protein. 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. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... A genetic disorder, or genetic disease is a disease caused, at least in part, by the genes of the person with the disease. ...

Often, gene mutations that could cause a genetic disorder are repaired by the cell's DNA repair enzymes before the gene is expressed (makes a protein). 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. DNA damage resulting in multiple broken chromosomes DNA repair is a process constantly operating in each cell of a living being; it is essential to survival because it protects the genome from damage. ...

See also

• Homeobox
• Macromutation
• Mutant

A homeobox is a stretch of DNA sequence found in genes involved in the regulation of the development (morphogenesis) of animals, fungi and plants. ... Most biologists believe that adaptation occurs through the accumulation of small mutations. ... This article is concerns biological mutants; for fictional aspects see Mutant (fictional) A mutant is an individual, organism, or new genetic character arising or resulting from an instance of mutation, which is a sudden structural change within the DNA of a gene or chromosome of an organism resulting in the...

References

• Maki H. 2002. Origins of spontaneous mutations: specificity and directionality of base-substitution, frameshift, and sequence-substitution mutageneses. Annual Review of Genetics 36:279-303.

External links

• The mutations chapter of the WikiBooks General Biology textbook
• EvoWiki: Mutation (http://www.evowiki.org/index.php/Mutation)