TRYPSIN QIAGEN TRYPSIN-QIAGEN
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Liquid Semen: Total DNA v. Extraction Method
Figure 9: Comparison of the three extraction methods on liquid semen.
Dried Semen, No Fabric: Total DNA v. Extraction Method
Figure 10: Comparison of the three extraction methods on semen dried in tubes without fabric.
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Dried Semen on White Cotton: Total DNA v. Extraction Method
25 4. CONCLUSIONS AND FUTURE DIRECTIONS
The research conducted in this study determined that the application of trypsin to the forensicGEM procedure is an effective method to extract DNA from dried semen stains present on different substrates. The amount of DNA extracted by the
trypsin/ZyGEM method was considerably higher than the amount of DNA extracted by the modified Qiagen® method. The use of Qiagen® directly on a trypsin/ZyGEM DNA extract showed a significant loss of sperm DNA. Qiagen® is a purification process that removes excess proteins and other cellular material by the use of silica columns and several washes. This may account for the loss DNA between the two different methods.
Future research should focus on the sensitivity of the T/Z method on varying amounts of dried semen, as well as the effects of sample age and DNA degradation. The method requires optimization and validation on single source samples before being applied to samples containing sperm DNA and non-sperm DNA in different ratios. Substrates regularly found in sexual assault evidence should also be tested. The use of this modified extraction method could eventually be adapted to automation, aiding in the potential to streamline the entire process of DNA analysis in forensic laboratories.
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