engleski

Effect of sunlight on bloodstain evidence collected from different surfaces

To investigate the effect of sunlight exposure and substrate type on degradation of DNA samples taken from blood stains placed on seven different surfaces: galvanized sheet, iron rod, newspaper, white print paper, glass, soil and ceramic panel during a period of four weeks. Methods Blood sample obtained from a single male donor was placed on 7 different surfaces and kept at room temperature during a 4 week summer period. Every 7 days 1 mm² of blood sample was collected from each substrate and stored in labeled tube for later analysis. DNA was extracted by the Chelex method, amplified using AmpFISTR Minifiler Plus Amplification Kit and quantified using Quantifiler Human DNA Quantification kit. After 7 days of the sun exposure, the highest amount of DNA was determined from a galvanized sheet stain, further from a ceramic panel, glass, newspaper, iron rod and white print paper surface. As expected, the amount of quantified DNA from all samples decreased as sunlight exposure time progressed. The obtained results, after the amplification in MiniFiler system, were in correlation with the DNA amount, measured by QRT-PCR method for all samples, except for soil and white print paper samples. The obtained data show that DNA degradation is correlated to the length of sunlight exposure and to the type of media the samples are taken from. A negative QRT-PCR result does not mean negative PCR amplification in STR system, therefore, both methods should be applied when analysing forensic samples collected from trace evidence.

forensic DNA ; crime bloodstains ; sunlight exposure ; DNA damage ; surface type

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