Forensic DNA analysis
While most well known as a tool in forensic investigations, DNA profiling can also be used for non-forensic purposes such as paternity testing and human genealogy research.
[1] A year after his discovery, Jefferys was asked to use his new found DNA analysis to convict a man that police believed was responsible for 2 rape murders.
However, RFLP was an inefficient process due to the fact that it used up large amounts of DNA which could not always be obtained from a crime scene.
Not only does STR analysis use less of a sample to analyze DNA, but it also is a part of a larger process called Polymerase Chain Reaction (PCR).
[10] Developed in 1991,[10] DQ alpha testing was the first forensic DNA technique that utilized the polymerase chain reaction.
[12] The DQ alpha 1 locus (or location) was also polymorphic and had multiple different alleles that could be used to limit the pool of individuals that could have produced that result and increasing the probability of exclusion.
[14] By 1995, scientists attempted to return to a VNTR based analysis combined with PCR technology called amplified fragment length polymorphisms (AmpFLP).
[8] It was hoped that this technique would allow for the discriminating power of RFLP analysis with the ability to process samples that have less template DNA to work with or which were otherwise degraded.
STR analysis builds upon RFLP and AmpFLP used in the past by shrinking the size of the repeat units, to 2 to 6 base pairs, and by combining multiple different loci into one PCR reaction.
These multiplexing assay kits can produce allele values for dozens of different loci throughout the genome simultaneously limiting the amount of time it takes to gain a full, individualizing, profile.
However, science is getting closer to creating a full DNA profile using STR analysis on single cells.
These instruments are being looked at for use in the offender booking process allowing police officers to obtain the DNA profile of the person under arrest.
Recently, the Rapid DNA Act of 2017 was passed in the United States, directing the FBI to create protocols for the implementation of this technology throughout the country.
However, multiple police agencies already use Rapid DNA instruments to collect samples from people arrested in their area.
Theoretically MPS has the ability to distinguish between identical twins as random point mutations would be seen within repeat segments that would not be picked up by traditional STR analysis.
This type of match statistic is easy to explain in a courtroom setting to individuals who have no scientific background but it also loses a lot of discriminating power as it does not take into account the suspect's genotype.
These calculations are repeated for all available loci with all available data and then each value is multiplied together to get the total combined probability of inclusion or exclusion.
The drawbacks with using likelihood ratios is that they are very difficult to understand how analysts arrived at a specific value and the mathematics involved get very complicated as more data is introduced to the equations.
