Collecting and analyzing DNA evidence from fingernails: a comparative study.

Area of Science:

• Forensic science
• Molecular biology
• Genetics

Background:

• Fingernail evidence is crucial in forensic investigations.
• Standardized methods for processing fingernail evidence are lacking.
• Exogenous DNA recovery from fingernails presents challenges.

Purpose of the Study:

• To evaluate various techniques for processing fingernail evidence.
• To optimize DNA extraction and STR analysis from fingernails.
• To assess the impact of different collection and transport methods on DNA yield and profile quality.

Main Methods:

• Analysis of fingernails with applied blood or epithelial cells.
• Comparison of soaking, swabbing, and scraping collection methods.
• Evaluation of silica-based versus organic DNA extraction kits.
• Assessment of DNA purification and Short Tandem Repeat (STR) analysis.
• Investigation of cross-contamination and cell loss during transport.

Main Results:

• Soaking or swabbing yielded autosomal STR mixtures; scrapings produced fewer mixtures but showed allelic dropout.
• Y-STR analysis provided single-source profiles, with scrapings also exhibiting dropout.
• Silica-based extraction recovered significantly more exogenous DNA than organic extraction, unaffected by nail polish.
• Successive swabbing led to cross-contamination, while transporting nails together reduced contamination but caused cell loss.
• Optimized processing enabled complete Y-STR profiles from male volunteers on female fingernails after scratchings.

Conclusions:

• Optimized fingernail processing protocols enhance exogenous DNA recovery and STR profile quality.
• Silica-based DNA extraction is superior for fingernail evidence.
• Specific collection and transport methods impact mixture generation and dropout rates.
• Effective Y-STR profiling is achievable with optimized fingernail analysis techniques.