Changes

                  

                  

In [[biology]], '''mutations''' are  changes to the [[base pair]] sequence of [[genetic material]] (either [[DNA]] or [[RNA]]). Mutations can be caused by copying errors in the genetic material during [[cell division]] and by exposure to [[ultraviolet]] or [[ionizing radiation|ionizing]] radiation, chemical [[mutagens]], or [[virus (biology)|viruses]], or can occur deliberately under cellular control during processes such as [[meiosis]] or [[hypermutation]]. In multicellular organisms, mutations can be subdivided into ''[[germline mutation]]s'', which can be passed on to descendants, and ''[[somatic mutation]]s''. The somatic mutations cannot be transmitted to descendants in animals. Plants sometimes can transmit somatic mutations to their descendants asexually or sexually (in case when flower buds develop in somatically mutated part of plant).

In [[biology]], '''mutations''' are  changes to the [[base pair]] sequence of [[genetic material]] (either [[DNA]] or [[RNA]]). Mutations can be caused by copying errors in the genetic material during [[cell division]] and by exposure to [[ultraviolet]] or [[ionizing radiation|ionizing]] radiation, chemical [[mutagens]], or [[virus (biology)|viruses]], or can occur deliberately under cellular control during processes such as [[meiosis]] or [[hypermutation]]. In multicellular organisms, mutations can be subdivided into ''[[germline mutation]]s'', which can be passed on to descendants, and ''[[somatic mutation]]s''. The somatic mutations cannot be transmitted to descendants in animals. Plants sometimes can transmit somatic mutations to their descendants asexually or sexually (in case when flower buds develop in somatically mutated part of plant).

==Classification==

==Classification==

===By effect on structure===

===By effect on structure===

The sequence of a gene can be altered in a number of ways. Gene mutations have varying effects on health depending on where they occur and whether they alter the function of essential proteins. Structurally, mutations can be classified as:

The sequence of a gene can be altered in a number of ways. Gene mutations have varying effects on health depending on where they occur and whether they alter the function of essential proteins. Structurally, mutations can be classified as:

* '''Loss-of-function mutations''' are the result of gene product having less or no function. When the allele has a complete loss of function ([[null allele]]) it is often called an '''[[Muller's morphs|amorphic]] mutation'''. Phenotypes associated with such mutations are most often [[recessive]]. Exceptions are when the organism is [[haploid]], or when the reduced dosage of a normal gene product is not enough for a normal phenotype (this is called [[haploinsufficiency]]).

* '''Loss-of-function mutations''' are the result of gene product having less or no function. When the allele has a complete loss of function ([[null allele]]) it is often called an '''[[Muller's morphs|amorphic]] mutation'''. Phenotypes associated with such mutations are most often [[recessive]]. Exceptions are when the organism is [[haploid]], or when the reduced dosage of a normal gene product is not enough for a normal phenotype (this is called [[haploinsufficiency]]).

* '''Gain-of-function mutations''' change the gene product such that it gains a new and abnormal function. These mutations usually have [[dominant gene|dominant]] phenotypes. Often called a [[Muller's morphs|neomorphic]] mutation.

* '''Gain-of-function mutations''' change the gene product such that it gains a new and abnormal function. These mutations usually have [[dominant gene|dominant]] phenotypes. Often called a [[Muller's morphs|neomorphic]] mutation.

* '''Dominant negative mutations''' (also called '''[[Muller's morphs|antimorphic]] mutations''') have an altered gene product that acts antagonistically to the wild-type allele. These mutations usually result in an altered molecular function (often inactive) and are characterised by a [[Dominant gene|dominant]] or [[incomplete dominance|semi-dominant]] phenotype. In humans, [[Marfan syndrome]] is an example of a dominant negative mutation occurring in an [[autosomal dominant]] disease. In this condition, the defective glycoprotein product of the fibrillin gene (FBN1) antagonizes the product of the normal allele.

* '''Dominant negative mutations''' (also called '''[[Muller's morphs|antimorphic]] mutations''') have an altered gene product that acts antagonistically to the wild-type allele. These mutations usually result in an altered molecular function (often inactive) and are characterized by a [[Dominant gene|dominant]] or [[incomplete dominance|semi-dominant]] phenotype. In humans, [[Marfan syndrome]] is an example of a dominant negative mutation occurring in an [[autosomal dominant]] disease. In this condition, the defective glycoprotein product of the fibrillin gene (FBN1) antagonizes the product of the normal allele.

*'''Lethal mutations''' are mutations that lead to a phenotype incapable of effective reproduction.

*'''Lethal mutations''' are mutations that lead to a phenotype incapable of effective reproduction.

===Special classes===

===Special classes===

*'''Conditional mutation''' is a mutation that has wild-type (or less severe) phenotype under certain "permissive" environmental conditions and a mutant phenotype under certain "restrictive" conditions. For example, a temperature-sensitive mutation can cause cell death at high temperature (restrictive condition), but might have no deletirious consequences at a lower temperature (permissive condition).

*'''Conditional mutation''' is a mutation that has wild-type (or less severe) phenotype under certain "permissive" environmental conditions and a mutant phenotype under certain "restrictive" conditions. For example, a temperature-sensitive mutation can cause cell death at high temperature (restrictive condition), but might have no deleterious consequences at a lower temperature (permissive condition).

===Causes of mutation===

===Causes of mutation===

Two classes of mutations are spontaneous mutations (molecular decay) and induced mutations caused by [[mutagen]]s.  

Two classes of mutations are spontaneous mutations (molecular decay) and induced mutations caused by [[mutagen]]s.  

'''Spontaneous mutations''' on the molecular level include:

'''Spontaneous mutations''' on the molecular level include:

* [[Tautomerism]] - A base is changed by the repositioning of a hydrogen atom.

* Tautomerism - A base is changed by the repositioning of a hydrogen atom.

* [[Depurination]] - Loss of a purine base (A or G).

* Depurination - Loss of a purine base (A or G).

* [[Deamination]] - Changes a normal base to an atypical base; C → U, (which can be corrected by DNA repair mechanisms), or spontaneous deamination of 5-methycytosine (irreparable), or A → HX (hypoxanthine).

* Deamination - Changes a normal base to an atypical base; C → U, (which can be corrected by DNA repair mechanisms), or spontaneous deamination of 5-methycytosine (irreparable), or A → HX (hypoxanthine).

* Transition - A purine changes to another purine, or a pyrimidine to a pyrimidine.

* Transition - A purine changes to another purine, or a pyrimidine to a pyrimidine.

* Transversion - A purine becomes a pyrimidine, or vice versa.

* Transversion - A purine becomes a pyrimidine, or vice versa.

'''Induced mutations''' on the molecular level can be caused by:

'''Induced mutations''' on the molecular level can be caused by:

==Beneficial mutations==

==Beneficial mutations==

A very small percentage of all mutations actually have a positive effect. These mutations lead to new versions of proteins that help an organism and its future generations better adapt to changes in their environment. For example, a specfic 32 base pair deletion in human CCR5 (CCR5-32) confers [[HIV]] resistance to [[Zygosity|homozygotes]] and delays [[AIDS]] onset in [[Zygosity|heterozygotes]].<ref>[http://www.cdc.gov/genomics/hugenet/factsheets/FS_CCR5.htm]</ref> The CCR5 mutation is more common in those of European descent. One theory for the [[etiology]] of the relatively high frequency of CCR5-32 in the euopean population is that is conferred resistance to the [[bubonic plague]] in mid-14th century Europe.<ref>[http://www.pbs.org/wnet/secrets/case_plague/clues.html]</ref>

A very small percentage of all mutations actually have a positive effect. These mutations lead to new versions of proteins that help an organism and its future generations better adapt to changes in their environment. For example, a specific 32 base pair deletion in human CCR5 (CCR5-32) confers [[HIV]] resistance to [[Zygosity|homozygotes]] and delays [[AIDS]] onset in [[Zygosity|heterozygotes]].<ref>[http://www.cdc.gov/genomics/hugenet/factsheets/FS_CCR5.htm]</ref> The CCR5 mutation is more common in those of European descent. One theory for the [[etiology]] of the relatively high frequency of CCR5-32 in the European population is that is conferred resistance to the [[bubonic plague]] in mid-14th century Europe.<ref>[http://www.pbs.org/wnet/secrets/case_plague/clues.html]</ref>

 

==References==

==References==

* [http://www.gate.net/~rwms/EvoMutations.html Examples of Beneficial Mutations]

* [http://www.gate.net/~rwms/EvoMutations.html Examples of Beneficial Mutations]

* [http://www.q-pharm.com/home/contents/drug_d/order_form/online_services/mutagenesis  Software for Mutated Proteins' Activity Prediction]

* [http://www.q-pharm.com/home/contents/drug_d/order_form/online_services/mutagenesis  Software for Mutated Proteins' Activity Prediction]

[[Category:Genetics]]

[[Category:Genetics]]