Forensic molecular Bioogy
DNA evidence is crucial for determining innocence or guilt in a crime, its collection at a crime scene must be performed to scrupulously high standards.
Human DNA sources
*Taken direct from suspects or in mass screens for elimination or from a known source.
*Red blood cells anucleate .*All white blood cells contain nuclear DNA.*Invasive
*Sloughed off epithelial cells from the inside of the buccalcavity. * Retrieved with swab •*Non-invasive
*Many follicle cells when pulled *Shed hairs less useful *Good reference for missing or unidentified person-sample from brush or home environment
DNA evidence collection
•Prevention of contamination is key,particular care must be taken :
- From collecting officers
- –Full protective SOCO suits essential
- –Elimination of officers DNA profiles
Presumptive testing for evidence
• Wherever fingerprints may be found • Wherever cells can collect
* Under fingernails; on clothing and footwear; plasters; toothbrushes; envelopes;
Preservation of evidence
Prevention of microbial degradation
* Dry and at low temperature
* 20°C to -70°C for long term
* Dry on proprietary cards…
-Proprietary cards such as FTA cards
* FTA Cards contain chemicals that lyse cells, denature proteins and protect nucleic acids from nucleases, oxidation and UV damage.
• DNA is separated from other cellular components
• The amount extracted is measured
– To see if sufficient is present for typing
– To determine how much should be used
– Quality can also be determined
Testing Dna Extract
• Agarose gels – Quantity and how intact?
• UV spectrophotometry – 260nm; 260/280 ratio; 260/230 ratio
• Pico green fluorescence spectrophotometry – Detects down to 25pg/ml DNA
• Real time PCR