Problems associated with the DNA analysis of stains.

Selected stain cases are presented which highlight various problems associated with DNA investigations on stain materials, especially risks of artefacts. These cases involve stain materials (blood, semen) which were exposed to different external conditions so that the DNA was partially degraded and of variable quantity. One multi locus probe (MLP) and 4-6 single locus probes (SLP's) were used for individualisation but artefacts such as extra bands, band deficiencies or shifts only occurred with the MLP. In one case where only a few spermatozoa were present in the vaginal swab, DNA extraction was carried out without preferential lysis to avoid loss of sperm DNA. The resulting mixed band pattern could be clearly attributed to the bands from the corresponding blood samples after SLP hybridisation.