Abstract: Objective To evaluate the validity of Differential Extraction Kit in isolating spermatozoa and epithelial cell DNA from mixture samples. Methods Selective lysis of spermatid and epithelial cells combined with paramagnetic particle method were applied to extract the DNA from the mock samples under controlled conditions and forensic case samples, and template DNA were analyzed by STR genotype method. Results This Differential Extraction Kit is efficient to obtain high quality spermatid and epithelial cell DNA from the mixture samples with different proportion of sperm to epithelial cell. Conclusion The Differential Extraction Kit can be applied in DNA extraction for mixed stain from forensic sexual assault samples.

Key words: forensic genetics, reagent kits, diagnostic, sex offenses, differential extraction, mixed stain