Problems associated with the DNA analysis of stains

Area of Science:

• Forensic Science
• Molecular Biology
• Genetics

Background:

• DNA analysis of biological stain materials (blood, semen) is crucial in forensic investigations.
• External factors can degrade DNA, leading to variable quantity and quality in stain samples.
• Artefacts in DNA profiling can compromise accurate individualisation and interpretation of results.

Purpose of the Study:

• To highlight problems and risks of artefacts in DNA investigations on stain materials.
• To compare the performance of multi-locus probes (MLPs) and single-locus probes (SLPs) with degraded DNA.
• To demonstrate reliable DNA individualisation strategies for challenging forensic samples.

Main Methods:

• Analysis of selected stain cases involving blood and semen exposed to various external conditions.
• DNA extraction and profiling using one multi-locus probe (MLP) and 4-6 single-locus probes (SLPs).
• Specific DNA extraction method employed for samples with limited spermatozoa to prevent DNA loss.

Main Results:

• Artefacts, including extra bands, band deficiencies, and shifts, were observed exclusively with the MLP.
• SLPs demonstrated reliable individualisation capabilities, even with partially degraded DNA of variable quantity.
• A mixed DNA profile from a vaginal swab with few spermatozoa was successfully resolved using SLPs, distinguishing sperm DNA from other sources.

Conclusions:

• MLPs are more susceptible to generating artefacts when analysing degraded DNA from stain materials.
• SLPs offer a more robust and reliable method for DNA individualisation in forensic casework with compromised samples.
• Careful selection of DNA profiling techniques and extraction methods is essential for accurate results with challenging forensic evidence.