What is DNA and how is a DNA profile generated?
DNA, or deoxyribonucleic acid, is a double helix shaped molecule that occurs inside every cell of a living organism and contains our unique genetic instructions to develop, live and reproduce.
These biological instructions are passed down from parents to offspring during reproduction. DNA can be extracted from a range of sources including blood, hair, skin, tissue, saliva, semen, teeth, nails and bone.
The automated DNA analytical processing system at FASS can load samples, collected by Police at the crime scene or in the FASS Evidence Recovery unit, using a specialised Robot Ready tube, directly onto a robotic platform to commence automated processing.
More complicated steps are required for other sample types which might require separation of different cell types during the extraction steps. Person reference samples are processed using a simplified semi-automated process. Video of DNA profile extraction processes at the FASS laboratory can be viewed here.
A DNA crime sample will take approximately two days to generate a DNA profile.
The steps typically include:
- Lysis: Cell and nucleus is broken down to release DNA
- Extraction: Purification of DNA using magnetic bead technology
- Quantitation: Estimation of much DNA has been recovered, the proportion of male DNA and the quality of the DNA.
- Amplification: Copies specific regions of DNA that are highly variable between individuals
- Capillary Electrophoresis: Uses genetic analysers to separate DNA fragments based on size
- Software analysis to determine the DNA types and profile
In cases of unidentified human remains, DNA is most likely to be extracted from bone rather than soft tissue as bone provides more protection against degradation following environmental exposure, and frequently more manually examination is required for these challenging samples.
During DNA extraction from skeletal remains, a small piece of bone is mechanically pulverised and dissolved in a solution which enables the DNA to be released. This is called demineralisation. A series of automated steps are then taken to purify the DNA and analyse it to determine the DNA profile of the individual. The time taken to recover a DNA profile is strongly influenced by the condition of the remains and typically ranges from a couple of days up to a week.
Remains that have been subjected to fire, salt water or extended environmental exposure can be challenging, however the methods used at the Forensic & Analytical Science Service to extract and analyse DNA have proved to be highly successful.
Even though the Forensic Biology/DNA laboratory is highly automated, DNA analysis of unidentified human remains often requires more intense handling and the use of manual processes to optimise the chance of recovering DNA profiles. Specialised contamination management processes are required.