Effects of 10% Unbuffered Formalin Fixation Time on STR Detection in Human Skeleton

To evaluate the effect of 10% unbuffered formalin fxation time on STR detection of human skeleton, in the paper fve skeletons were selected, and the backbone segments were divided into 12 segments using a chainsaw. The backbone segments were soaked in a 10% unbuffered formalin solution at room temperature, and samples were taken at various time intervals. DNA was quantifed using QuantiFiler^® Trio DNA Quantification Kit. PCR amplification was performed using IDentifer DNA typing kit (Yanhuang 34) and SureID^®X37 Human X-STR kit, and STR data was obtained using 3500xL genetic analyzer. The results showed that fxation time of skeletons was inversely proportional to the DNA mass concentration and proportional to the DNA degradation index. Full STR profle could be obtained by autosomal and X chromosome tests on skeletons fxed within 10 days in 10% unbuffered formalin. For samples fxed for a period of 22 days, the STR detection rate could be maintained above 77.33%. When the fxed time was extended to 30 days, the allele detection rate of samples was significantly reduced to less than 30%. Finally, when the fxed time had reached 60 days, the DNA quantitative results in all samples dropped below 0.02 ng/μL, and only a few samples yielded sporadic STR genotypes for small fragments. In conclusion, the fxation time in 10% unbuffered formalin affects DNA quality extracted from human skeletons and is thus an important factor affecting the STR detection rate.