Editing DNA profiling (section)

===Low-Template DNA===
Low-template DNA can happen when there is less than 0.1&nbsp;ng(<ref>{{cite book |last1=Butler |first1=John M. |title=Forensic DNA typing : biology, technology, and genetics of STR markers |date=2005 |publisher=Elsevier Academic Press |location=Amsterdam |isbn=978-0-12-147952-7 |pages=68, 167–168 |edition=2nd}}</ref>) of DNA in a sample. This can lead to more stochastic effects (random events) such as allelic dropout or allelic drop-in which can alter the interpretation of a DNA profile. These stochastic effects can lead to the unequal amplification of the 2 alleles that come from a heterozygous individual. It is especially important to take low-template DNA into account when dealing with a mixture of DNA sample. This is because for one (or more) of the contributors in the mixture, they are more likely to have less than the optimal amount of DNA for the PCR reaction to work properly.<ref>{{cite book |last1=Butler |first1=John M. |title=Advanced topics in forensic DNA typing : interpretation |date=2015 |publisher=Academic Press |location=Oxford, England |isbn=978-0-12-405213-0 |pages=159–161}}</ref> Therefore, stochastic thresholds are developed for DNA profile interpretation. The stochastic threshold is the minimum peak height (RFU value), seen in an electropherogram where dropout occurs. If the peak height value is above this threshold, then it is reasonable to assume that allelic dropout has not occurred. For example, if only 1 peak is seen for a particular locus in the electropherogram but its peak height is above the stochastic threshold, then we can reasonably assume that this individual is homozygous and is not missing its heterozygous partner allele that otherwise would have dropped out due to having low-template DNA. Allelic dropout can occur when there is low-template DNA because there is such little DNA to start with that at this locus the contributor to the DNA sample (or mixture) is a true heterozygote but the other allele is not amplified and so it would be lost. Allelic drop-in<ref>{{cite journal |last1=Gittelson |first1=S |last2=Steffen |first2=CR |last3=Coble |first3=MD |title=Low-template DNA: A single DNA analysis or two replicates? |journal=Forensic Science International |date=July 2016 |volume=264 |pages=139–45 |doi=10.1016/j.forsciint.2016.04.012 |pmid=27131143 |pmc=5225751 }}</ref> can also occur when there is low-template DNA because sometimes the stutter peak can be amplified. The stutter is an artifact of PCR. During the PCR reaction, DNA Polymerase will come in and add nucleotides off of the primer, but this whole process is very dynamic, meaning that the DNA Polymerase is constantly binding, popping off and then rebinding. Therefore, sometimes DNA Polymerase will rejoin at the short tandem repeat ahead of it, leading to a short tandem repeat that is 1 repeat less than the template. During PCR, if DNA Polymerase happens to bind to a locus in stutter and starts to amplify it to make lots of copies, then this stutter product will appear randomly in the electropherogram, leading to allelic drop-in.

====MiniSTR analysis====
In instances in which DNA samples are degraded, like if there are intense fires or all that remains are bone fragments, standard STR testing on those samples can be inadequate. When standard STR testing is done on highly degraded samples, the larger STR loci often drop out, and only partial DNA profiles are obtained. Partial DNA profiles can be a powerful tool, but the probability of a random match is larger than if a full profile was obtained. One method that has been developed to analyse degraded DNA samples is to use miniSTR technology. In the new approach, primers are specially designed to bind closer to the STR region.<ref name="Coble 2005">{{cite journal | vauthors = Coble MD, Butler JM | title = Characterization of new miniSTR loci to aid analysis of degraded DNA | journal = Journal of Forensic Sciences | volume = 50 | issue = 1 | pages = 43–53 | date = January 2005 | pmid = 15830996 | doi = 10.1520/JFS2004216 | url = https://strbase.nist.gov/pub_pres/Coble2005miniSTR.pdf | access-date = 24 November 2018 | url-status = live | archive-url = https://web.archive.org/web/20170907224005/http://strbase.nist.gov/pub_pres/Coble2005miniSTR.pdf | archive-date = 7 September 2017}}</ref>

In normal STR testing, the primers bind to longer sequences that contain the STR region within the segment. MiniSTR analysis, however, targets only the STR location, which results in a DNA product that is much smaller.<ref name="Coble 2005"/>

By placing the primers closer to the actual STR regions, there is a higher chance that successful amplification of this region will occur. Successful amplification of those STR regions can now occur, and more complete DNA profiles can be obtained.  The success that smaller PCR products produce a higher success rate with highly degraded samples was first reported in 1995, when miniSTR technology was used to identify victims of the Waco fire.<ref>{{cite journal | vauthors = Whitaker JP, Clayton TM, Urquhart AJ, Millican ES, Downes TJ, Kimpton CP, Gill P | title = Short tandem repeat typing of bodies from a mass disaster: high success rate and characteristic amplification patterns in highly degraded samples | journal = BioTechniques | volume = 18 | issue = 4 | pages = 670–677 | date = April 1995 | pmid = 7598902 }}</ref>