Abstract: Objective To explore the effect on DNA quantification and STR typing from cigarette butts collected at different time points. Methods Forty "Hongshuangxi" brand cigarette butts smoked by ten different individuals(4 cigarettes per individual) were collected. DNA was extracted from the outer layer and the sponge of the cigarette butts using chelex-100 extraction kit, as well as STR typing and DNA quantitation were simultaneously performed in 1, 4, 7 and 10 weeks, respectively. Results The DNA quantities extracted from the outer layer at the 1st, 4th, 7th and 10th week were 0.104-2.52, 0.110-2.41, 0.096 02.32 and 0.085 0-2.28 ng/μL, while the detection rates for 16 loci by STR typing were 100%, 90%, 75% and 62.5%, respectively. The DNA quantities extracted from the sponge were 0.018 0-2.40, 0.017 1-2.25, 0.016 5-2.15 and 0.016 0-2.15 ng/μL, while the detection rates for 16 loci by STR typing were 97.5%, 82.5%, 50% and 12.5%, respectively. Conclusion There is little difference in DNA quantity between the outer layer and the sponge of butts during 10 weeks, but there is an obvious effect on STR typing with prolonged extracting time. There is a much more effect on the sponge than on the outer layer, and the longer the standing time is, the lower the detection rate is.

Key words: forensic genetics, mouth mucosa, cell extracts, cigarette butt, DNA quantification, STR typing