Editing DNA profiling (section)

===STR analysis===
[[File:Short Tandem Repeat (STR) analysis.png|thumb|300px|Short Tandem Repeat (STR) analysis on a simplified model: First, a DNA sample undergoes [[polymerase chain reaction]] with [[Primer (molecular biology)|primers]] targeting certain STRs (which vary in lengths between individuals and their [[allele]]s). The resultant fragments are separated by size (such as [[electrophoresis]]).<ref>Image by Mikael Häggström, using following source image: [https://www.researchgate.net/figure/Principles-of-STR-analysis-STRs-loci-comprise-repetitive-sequences-of-2-7-bp-which-are_fig1_26513043 Figure 1 - available via license: Creative Commons Attribution 4.0 International"], from the following article:<br>{{cite journal|title=Using PCR for molecular monitoring of post-transplantation chimerism|url=https://www.researchgate.net/publication/26513043|first1=Roberta |last1=Sitnik|first2= Margareth Afonso|last2= Torres|first3= Nydia |last3=Strachman Bacal|first4= João Renato Rebello |last4=Pinho|journal=Einstein (Sao Paulo)|year=2006|volume=4|issue=2|s2cid=204763685}}</ref>]]
{{Main|STR analysis}}
The system of DNA profiling used today is based on [[polymerase chain reaction]] (PCR) and uses simple sequences.<ref name="Tautz2"/>

From country to country, different STR-based DNA-profiling systems are in use. In North America, systems that amplify the [[CODIS]] 20<ref>{{Cite web|url=https://www.fbi.gov/services/laboratory/biometric-analysis/codis|title=Combined DNA Index System (CODIS)|website=Federal Bureau of Investigation|language=en-us|access-date=20 April 2017|archive-date=29 April 2017|archive-url=https://web.archive.org/web/20170429154144/https://www.fbi.gov/services/laboratory/biometric-analysis/codis|url-status=live}}</ref> core loci are almost universal, whereas in the United Kingdom the [[DNA-17]] loci system is in use, and Australia uses 18 core markers.<ref>{{Cite news|url=https://theconversation.com/from-the-crime-scene-to-the-courtroom-the-journey-of-a-dna-sample-82250|title=From the crime scene to the courtroom: the journey of a DNA sample| vauthors = Curtis C, Hereward J |date=29 August 2017|work=The Conversastion|access-date=14 October 2017|archive-date=25 July 2018|archive-url= https://web.archive.org/web/20180725203821/http://theconversation.com/from-the-crime-scene-to-the-courtroom-the-journey-of-a-dna-sample-82250|url-status=live}}</ref>

The true power of [[STR analysis]] is in its statistical power of discrimination. Because the 20 loci that are currently used for discrimination in CODIS are [[independent assortment|independently assorted]] (having a certain number of repeats at one locus does not change the likelihood of having any number of repeats at any other locus), the [[Probability#Independent events|product rule for probabilities]] can be applied. This means that, if someone has the DNA type of ABC, where the three loci were independent, then the probability of that individual having that DNA type is the probability of having type A times the probability of having type B times the probability of having type C. This has resulted in the ability to generate match probabilities of 1 in a quintillion (1x10<sup>18</sup>) or more.{{explain|date=March 2022}} However, DNA database searches showed much more frequent than expected false DNA profile matches.<ref>{{Cite news| vauthors = Felch J |title = FBI resists scrutiny of 'matches'|newspaper = Los Angeles Times|pages = P8|date = 20 July 2008|url = https://www.latimes.com/archives/la-xpm-2008-jul-20-me-dna20-story.html|access-date = 18 March 2010|display-authors = etal|archive-date = 11 August 2011|archive-url = https://web.archive.org/web/20110811135116/http://articles.latimes.com/2008/jul/20/local/me-dna20|url-status = live}}</ref>