DNA Typing - PCRInvented 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

Primers recognize small pieces of DNA that are complimentary to specific sequences of bases in the DNA sample.

DNA Typing - PCR

HLA DG alpha system (now called DQA1) contains 28 different primers.

Polymarker (PM) has five additional genetic markers.

DNA Typing – PCR analysis

PCR

DNA Typing - STR

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.

DNA Typing - STRSTRs are locations (loci) on the chromosome that

contain short sequence elements that repeat themselves within the DNA molecule.

DNA Typing - STR

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.

DNA Typing - STR

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.

Y-STRs A set of specific STR markers associated with only

the male Y chromosome has recently been developed

Y-STR typing can unambiguously determine what a male has contributed to a mixed sample

Often used in rape investigations because it can distinguish male DNA from female DNA

Mitochondrial DNA

Mitochondrial DNA

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.

Mitochondrial DNA

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).

Mitochondrial DNA

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.

Mitochondrial DNA

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.

The Combined DNA Index System

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.

The Combined DNA Index System

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.

Abandoned DNA Police can offer suspect a drink or cigarette, then later

collect the DNA from the item without the suspect’s knowledge

The Fourth Amendment protects against “unreasonable search”

However, courts have ruled that DNA testing on abandoned items does not violate an individual’s reasonable expectation of privacy

Exonerations

As of May 2008, 216 post-conviction DNA exonerations have been made in the U.S.

The true perpetrators have been identified in 82 of the DNA exoneration cases

Preservation of evidence by state police is crucial to a DNA exoneration