Prevalence of Non-self DNA on Three Different Sebaceous Skin Locations

This project serves to provide additional information on the prevalence of non-self DNA on the exposed skin locations specifically the inner upper arm, the nape area of the neck and the neck area just below the ear, where current literature is lacking. Skin tape lifts from these locations were collected from 15 male participants and 13 female participants once a week over a period of three weeks. Only single source profiles were obtained from six volunteers. Eight volunteers had only one mixture DNA profile in nine samples, while mixture DNA profiles for at least two collection occasions were observed in 16 volunteers. The location of skin sample, gender and time of last shower were evaluated for their effect on the detection of non-self alleles. Analysis of variance (ANOVA) showed that none of the variables had a significant effect on the detection of non-self alleles. The mixture of DNA profiles across all datasets were closely examined for the presence of a repeating non-self genotype. Samples collected from the upper arm area presented the highest number of mixtures with non-self alleles being present more than once over the three weeks. A repeating non-self genotype was also observed in the neck area below the ear in one volunteer. For three out of 28 volunteers, these repeating non-self genotypes across all three collection occasions could be attributed to a common contributor. No repeating genotypes were determined for the nape area of the neck. These findings can be meaningful in cases of sexual assault and manual strangulation, where information on the prevalence of non-self DNA on parts of the upper body is important