Editing Genotoxicity (section)

==''in vitro'' toxicology testing==
The purpose of ''[[in vitro]]'' testing is to determine whether a substrate, product, or environmental factor induces genetic damage.  One technique entails cytogenetic assays using different mammalian cells.<ref name="genotoxicity.testing" />  The types of [[chromosome abnormality|aberrations]] detected in cells affected by a genotoxic substance are chromatid and chromosome gaps, chromosome breaks, chromatid deletions, fragmentation, translocation, complex rearrangements, and many more. The [[clastogen]]ic or [[aneugen]]ic effects from the genotoxic damage will cause an increase in frequency of structural or numerical aberrations of the genetic material.<ref name="genotoxicity.testing" />  This is similar to the [[micronucleus test]] and chromosome aberration assay, which detect structural and numerical chromosomal aberrations in mammalian cells.<ref name="genotoxicity.carcinogenicity" />

In a specific mammalian tissue, one can perform a mouse [[lymphoma]] TK+/- assay to test for changes in the genetic material.<ref name="genotoxicity.testing" />  Gene mutations are commonly point mutations, altering only one base within the genetic sequence to alter the ensuing transcript and amino acid sequence; these point mutations include base substitutions, deletions, frame-shifts, and rearrangements.  Also, [[chromosome|chromosomes']] integrity may be altered through chromosome loss and clastogenic [[lesions]] causing multiple gene and multilocus deletions.  The specific type of damage is determined by the size of the colonies, distinguishing between genetic mutations (mutagens) and chromosomal aberrations (clastogens).<ref name="genotoxicity.testing" />

The [[SOS chromotest|SOS/umu assay test]] evaluates the ability of a substance to induce DNA damage; it is based on the alterations in the induction of the SOS response due to DNA damage.  The benefits of this technique are that it is a fast and simple method and convenient for numerous substances.  These techniques are performed on water and wastewater in the environment.<ref name="invitro.genotoxicitytesting">{{cite web |url=http://www.nib.si/eng/index.php/storitve-in-oprema/testi-genotoksinosti-in-vitro.html |title=In Vitro Genotoxicity Testing |last=Končar |first=Helena | name-list-style = vanc |year=2011 |publisher=National Institute of Biology |access-date=2013-03-16 |url-status=dead |archive-url=https://web.archive.org/web/20130307220932/http://www.nib.si/eng/index.php/storitve-in-oprema/testi-genotoksinosti-in-vitro.html |archive-date=2013-03-07 }}</ref>

[[File:Genotoxic Damage.png|500px|right|thumb|Overview of the use of the SOS response for genotoxicity testing]]

===''in vivo'' testing===
The purpose for ''[[in vivo]]'' testing is to determine the potential of DNA damage that can affect chromosomal structure or disturb the [[mitotic spindle|mitotic apparatus]] that changes chromosome number; the factors that could influence the genotoxicity are ADME and DNA repair.  It can also detect genotoxic agents missed in ''in vitro'' tests.  The positive result of induced chromosomal damage is an increase in frequency of micronucelated PCEs.<ref name="genotoxicity.testing" />  A [[micronucleus]] is a small structure separate from the nucleus containing nuclear DNA arisen from DNA fragments or whole chromosomes that were not incorporated in the daughter cell during mitosis.  Causes for this structure are mitotic loss of acentric chromosomal fragments (clastogenicity), mechanical problems from chromosomal breakage and exchange, mitotic loss of chromosomes (aneugenicity), and apoptosis.  The micronucleus test ''in vivo'' is similar to the ''in vitro'' one because it tests for structural and numerical chromosomal aberrations in mammalian cells, especially in rats' blood cells.<ref name="genotoxicity.testing" />

===Comet assay===
{{See also|Comet assay}}
[[Comet assay]]s are one of the most common tests for genotoxicity. The technique involves lysing cells using detergents and salts. The DNA released from the lysed cell is electrophoresed in an agarose gel under [[neutral pH]] conditions. Cells containing DNA with an increased number of double-strand breaks will migrate more quickly to the anode. This technique is advantageous in that it detects low levels of DNA damage, requires only a very small number of cells, is cheaper than many techniques, is easy to execute, and quickly displays results. However, it does not identify the mechanism underlying the genotoxic effect or the exact chemical or chemical component causing the breaks.<ref name="Tice">{{cite journal | vauthors = Tice RR, Agurell E, Anderson D, Burlinson B, Hartmann A, Kobayashi H, Miyamae Y, Rojas E, Ryu JC, Sasaki YF | display-authors = 6 | title = Single cell gel/comet assay: guidelines for in vitro and in vivo genetic toxicology testing | journal = Environmental and Molecular Mutagenesis | volume = 35 | issue = 3 | pages = 206–21 | year = 2000 | pmid = 10737956 | doi = 10.1002/(SICI)1098-2280(2000)35:3<206::AID-EM8>3.0.CO;2-J | url = http://cometassayindia.org/COMET%20ASSAY%20GUIDELINES.pdf | doi-access = free | bibcode = 2000EnvMM..35..206T }}</ref>