9-6 Collection and Preservation of Biological Evidence for DNA Analysis Unit 9: DNA

Biological Evidence Biological evidence should not be packaged in plastic or airtight containers because the accumulation of residual moisture can contribute to the growth of blood destroying bacteria fungi.

Packaging Biological Evidence Each article should be packed separately in a paper bag or in a well ventilated box. Tandem repeats. MLVA is a method used to perform molecular typing of microorganisms. It utilizes the naturally occurring variation in the number of tandem repeated DNA sequences found in the microbial genome of most bacterial species. Such tandem repeats may be perfect, but often imperfect repeats containing mutations are encountered.

RFLP The least intrusive method for obtaining DNA standard reference is the buccal swab.

DNA Collection In this procedure, cotton swabs are placed in the subject mouth and inside of the cheek is vigorously swabbed, resulting in the transfer of cells in the inner cheek lining to the swap.

Minimize Contamination To minimize contamination during the collection of biological evidence, the following steps should be taken.

Step 1 Change gloves before handling each new piece of evidence.

Step 2 Collect a substrate control for possible subsequent laboratory examination. Substrate control is an uncontaminated surface material close to an area where evidence was found.

Step 3 Pick up small Items of evidence such as cigarette butts and stamps with clean forceps. Disposable forceps are to be used so that they can be discarded after single evidence collection.

Step 4 Always package each item of evidence in its own well ventilated container.