DNA Typing - PCR. Invented in 1987. PCR offers the possibility of increased sensitivity. It requires 50 times less sample than RFLP analysis. DNA sample, DNA polymerases, nucleotides, and a primer are placed in a DNA Thermal Cycler. Discriminates to 1 in 5000. DNA Typing - PCR.
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Invented in 1987.
PCR offers the possibility of increased sensitivity. It requires 50 times less sample than RFLP analysis.
DNA sample, DNA polymerases, nucleotides, and a primer are placed in a DNA Thermal Cycler.
Discriminates to 1 in 5000.
Primers recognize small pieces of DNA that are complimentary to specific sequences of bases in the DNA sample.
HLA DG alpha system (now called DQA1) contains 28 different primers.
Polymarker (PM) has five additional genetic markers.
STR – Short Tandem Repeats
The newest method of DNA typing. The FBI started using it in 1998. Still in use today.
In combination with PCR (DQA1 and Polymarker) it is more discriminating (1 in 25,000,000) and less time consuming than RFLP. It also requires smaller sample sizes than RFLP.
STRs are locations (loci) on the chromosome that contain short sequence elements that repeat themselves within the DNA molecule.
The repeating sequence typically contains 3 to 7 bases.
The sequence can repeat 3 to 65 times.
HUMTH01 is a commonly used STR. It contains the A-A-T-G sequence. Seven variants (5 –11 repeats) have been identified in the human genome.
STRs can be amplified using PCR.
There are hundreds of different types of STRs that can be used for DNA typing.
Using more than one STR at a time is called multiplexing.
Nuclear DNA – 1 per cell
Mitochondria – 100 – 1000 per cell
mtDNA is inherited solely from your mother. Therefore, others in your family have the same mtDNA.
mtDNA has a loop configuration. It contains the information for 37 proteins.
Two regions are highly variant: Hypervariable Region 1 (HV1) and Hypervariable Region 2 (HV2).
The analytical technique of analysis of mtDNA, (sequencing), is very tedious, costly, and time consuming.
Therefore, only a few labs are equipped to analyze mtDNA.
Why do it then?
mtDNA can be obtained from hair, bones, and very small tissue samples.
mtDNA has been used to identify victims of mass destruction and unknown war victims.
CODIS – A national computerized database containing the results of DNA analysis of sex offenders.
The federal DNA Identification Act of 1994 initiated the nation wide project with $40 million in funding.
Currently, thirteen STRs are entered in to CODIS for each DNA entry.
The data base has been very effective in aiding investigators solve many crimes.