biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...

, and especially in

genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar wor ...

, a mutant is an organism or a new genetic character arising or resulting from an instance of

mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA replication, DNA or viral repl ...

, which is generally an alteration of the DNA sequence of the

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

of an

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...

. It is a characteristic that would not be observed naturally in a specimen. The term mutant is also applied to a

virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsk ...

with an alteration in its

nucleotide sequence A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. By convention, sequences are usu ...

whose

is in the

nuclear genome Nuclear DNA (nDNA), or nuclear deoxyribonucleic acid, is the DNA contained within each cell nucleus of a eukaryotic organism. It encodes for the majority of the genome in eukaryotes, with mitochondrial DNA and plastid DNA coding for the rest. I ...

. The natural occurrence of genetic mutations is integral to the process of

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

. The study of mutants is an integral part of biology; by understanding the effect that a mutation in a gene has, it is possible to establish the normal function of that gene.Clock Mutants of ''Drosophila melanogaster''
/ref>

Mutants arise by mutation

Mutants arise by

s occurring in pre-existing

s as a result of errors of

DNA replication In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritanc ...

or errors of

DNA repair DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA da ...

. Errors of replication often involve

translesion synthesis DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA dama ...

by a

DNA polymerase A DNA polymerase is a member of a family of enzymes that catalyze the synthesis of DNA molecules from nucleoside triphosphates, the molecular precursors of DNA. These enzymes are essential for DNA replication and usually work in groups to create ...

when it encounters and bypasses a damaged base in the template strand. A

DNA damage DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA d ...

is an abnormal chemical structure in DNA, such as a strand break or an oxidized base, whereas a mutation, by contrast, is a change in the sequence of standard base pairs. Errors of repair occur when repair processes inaccurately replace a damaged DNA sequence. The DNA repair process

microhomology-mediated end joining Microhomology-mediated end joining (MMEJ), also known as alternative nonhomologous end-joining (Alt-NHEJ) is one of the pathways for repairing double-strand breaks in DNA. As reviewed by McVey and Lee, the foremost distinguishing property of MMEJ ...

is particularly error-prone.

Etymology

Although not all mutations have a noticeable

phenotypic In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...

effect, the common usage of the word "mutant" is generally a

pejorative A pejorative or slur is a word or grammatical form expressing a negative or a disrespectful connotation, a low opinion, or a lack of respect toward someone or something. It is also used to express criticism, hostility, or disregard. Sometimes, a ...

term, only used for genetically or phenotypically noticeable mutations.Mutant. (n.d.). ''The American Heritage Dictionary of the English Language'', Fourth Edition. Retrieved March 05, 2008, from Dictionary.com
/ref> Previously, people used the word "sport" (related to spurt) to refer to abnormal specimens. The scientific usage is broader, referring to any organism differing from the

wild type The wild type (WT) is the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard "normal" allele at a locus, in contrast to that produced by a non-standard, "m ...

. The word finds its origin in the Latin term mūtant- (stem of mūtāns), which means "to change". Mutants should not be confused with organisms born with developmental abnormalities, which are caused by errors during

morphogenesis Morphogenesis (from the Greek ''morphê'' shape and ''genesis'' creation, literally "the generation of form") is the biological process that causes a cell, tissue or organism to develop its shape. It is one of three fundamental aspects of deve ...

. In a developmental abnormality, the DNA of the organism is unchanged and the abnormality cannot be passed on to progeny.

Conjoined twins Conjoined twins – sometimes popularly referred to as Siamese twins – are twins joined ''Uterus, in utero''. A very rare phenomenon, the occurrence is estimated to range from 1 in 49,000 births to 1 in 189,000 births, with a somewhat higher in ...

are the result of developmental abnormalities. Chemicals that cause developmental abnormalities are called teratogens; these may also cause mutations, but their effect on development is not related to mutations. Chemicals that induce mutations are called mutagens. Most mutagens are also considered to be

carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subs ...

Epigenetic alterations

Mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA replication, DNA or viral repl ...

s are distinctly different from epigenetic alterations, although they share some common features. Both arise as a

chromosomal A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

alteration that can be replicated and passed on to subsequent cell generations. Both, when occurring within a gene, may silence expression of the gene. Whereas mutant cell lineages arise as a change in the sequence of standard bases, epigenetically altered cell lineages retain the sequence of standard bases but have gene sequences with changed levels of expression that can be passed down to subsequent cell generations. Epigenetic alterations include methylation of

CpG islands The CpG sites or CG sites are regions of DNA where a cytosine nucleotide is followed by a guanine nucleotide in the linear sequence of bases along its 5' → 3' direction. CpG sites occur with high frequency in genomic regions called CpG isl ...

of a gene promoter as well as specific chromatin histone modifications. Faulty repair of chromosomes at sites of DNA damage can give rise both to mutant cell lineages and/or epigenetically altered cell lineages.

References

External links

{{Wikiquote
Antennapedia mutant
Evolutionary biology Classical genetics Mutation

Mutants arise by mutation

Etymology

Epigenetic alterations

See also

References

External links