ABSTRACT
Genotyping of biological samples is now routinely performed in human identication (HID) laboratories for applications like paternity testing, forensic casework, DNA databasing, missing persons testing, lineage studies, identication of remains, and so forth. e genotyping protocol comprises sample collection, extraction of DNA from the biological sample, quantication of the DNA, amplication of target loci, identication of amplied products, and the analysis of results. Extraction of DNA is the rst and most critical step of sample processing simply because a better quality and higher quantity of DNA leads to a higher quality, and likely more complete, genotype. Isolation of DNA from forensic samples is a challenging process that creates bottlenecks in the sample-processing work-ow. e challenges are primarily due to the nature of biological samples. Unlike most clinical samples, the biological samples processed in forensic laboratories vary widely and include biological uids (saliva, blood, and semen), tissues, hair, bone, tooth, nail, and so forth. Moreover, body uids can be deposited on a wide range of substrates (rather unlimited), mixed with inhibitors of the polymerase chain reaction (PCR), exposed to varying environmental conditions, or subjected to uncontrolled degradation, and they are oen present in limited quantities. Even the single-source samples processed for DNA databasing exhibit variation in the type of body uid (typically blood or saliva) and substrates. e spectrum of substrates on which biological samples get deposited expands dramatically for forensic evidence samples. Examples of the most common PCR inhibitors found in forensic samples include hematin from blood, humic acids from soil, textile dyes such as indigo from denim, calcium from bones, melanin from soil, and tannins from leather. e amount of DNA isolated from forensic samples cannot be predicted ahead of extraction because of the nature of these samples.
