| Summary: | 碩士 === 國立臺灣大學 === 法醫學研究所 === 99 === With the characteristics of hard structure and compositions, bone provides a good protection of DNA in bony tissue. In forensic cases, skeletal remains of victims are frequently recovered in various environments. Normally the DNA from remains is severely degraded, thereby affecting the effectiveness of DNA analysis. Based on previous literature, the influentical factors for DNA degradation in bony tissue are humidity, temperature or timing. However, there are no systematic studies on the observation of DNA degradation about bony tissue immersed in freshwater or seawater. The aim of this study was to investigate the degradation of DNA and the reliability of DNA identification on pig ribs and human ribs immersed in seawater or freshwater for different time periods and temperature. Bone specimens were prepared and submerged in freshwater and seawater respectively, then kept in both 4℃ and room-temperature (25℃). After different time periods of immersion, DNA was extracted by crushed procedure, followed by qPCR quantification and STR typing studied. If more than 8 STR loci were failed to amplify in the study of human ribs, 10-fold DNA template was used to re-analysis and mtDNA HV-1 DNA was sequenced. The results showed that the amounts of DNA extracted from both kinds of ribs immersed in freshwater or seawater were decreased with time periods. The STR typing was also worsend. However, for those with more compact bone such as pig ribs or both pig ribs and human ribs kept in 4℃, the trend of DNA degradation would be retaded. This indicated that the density of compact bone and environmental temperature were important factors in the DNA degradation of bony tissue. STR profiles could be obtained in human ribs immersed even after 8 months. It showed, however, only partial STR profiles were obtained and the STR loci with 300 bp in length were all poorly detected. For the highly degraded DNA samples, the detection of STR loci could be improved by raising the amount of DNA template in PCR reaction, or sequencing the mtDNA D-loop to assist victim identification.
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