Forensics – FAQ

Available Forms | FAQ | Evidence Guidelines

Q: What is the biology behind DNA Forensic testing?
Q: What are STRs that all the testing service talk about?
Q: Can you tell something about a person from forensic testing?
Q: What kind of sample is in needed for DNA forensic testing?
Q: What are the different methods of performing DNA forensic analysis?
Q: What is PCR?
Q: What is CODIS?
Q: What is mitochondrial DNA and how it is used in DNA forensics?

Q: What is the biology behind DNA Forensic testing?

A: The molecular biology of DNA forensic analysis was first developed by Dr. Alec Jeffreys (now Professor Sir Alec Jeffreys) for a sexual assault case in England. The terms ‘DNA Fingerprinting’ and ‘DNA profiling’ now all refer to the same technique.  Dr. Jeffreys discovered that the repeated DNA structures he was studying had the same core sequences: the variation he observed was unique to each individual.  When this approach was applied on a slightly larger scale, each individual would have a unique pattern, distinguishable from all others.  This forms the basis of current DNA forensic testing.

back to top

Q: What are STRs that are used for DNA forensics?

A: STRs is an acronym for Short Tandem Repeat.  These are genetic elements (sequences in the DNA) that are used  in forensic DNA analysis.   There are other genetic elements that can be used for determining identity, but STRs are considered the the most accurate and reliable method.  They are the only markers IFI uses.

back to top

Q: Can you tell something about a person from DNA forensic testing?

A: Actually no, there is no genetic, health or disease susceptibility information in DNA analysis using STRs.  It only provides an STR profile that can be used, in conjunction with a database, to positively identify an individual.

back to top

Q: What kind of sample is needed for DNA forensic testing?

A: The test requires DNA.  DNA can be extracted and analyzed from blood, semen, saliva, skin scrapings, hair, bones or teeth. Even minute amounts of material can be sufficient to obtain a DNA profile.

back to top

Q: What are the different methods of performing DNA forensic analysis?

A: To simplify a little,  the methods depend on which kind of laboratory instrument is used to obtain the STR profile.  All methods use PCR amplification in order to analyze STRs; IFI then uses an industry standard capillary electrophoresis instrument to analyze the results of the  amplification.

back to top

Q: What is PCR?

A: PCR is an acronym for Polymerase Chain Reaction.  This is the molecular biological technique that can amplify specific regions of DNA with great accuracy. Using this technique sufficient quantity of DNA can be produced in a few hours such that the STR profile can be determined.

back to top

Q: What is CODIS?

A: CODIS is an acronym for Combined DNA Index System. It is a searchable database maintained by the FBI (for further information, go to the CODIS home page) that contains more than 1,000,000 DNA profiles.

back to top

Q: What is mitochondrial DNA and how it is used in DNA forensics?

A: Most DNA forensic work uses genomic DNA: the genetic material within the nucleus of the cell.  Mitochondria are organelles (an intracellular compartment) that contain a small, circular genome that can also be used for genetic identification testing.  The methods and analysis of mitochondrial DNA are fundamentally different from genomic analysis: sequencevs. allele based, maternally inherited vs. Mendelian.  Mitochondrial DNA analysis is used particularly on old or degraded samples where STR analysis is likely to fail.

back to top

Available Forms | FAQ | Evidence Guidelines