DNA IDENTIFICATION

Human DNA Identification in Mass Disasters



Human DNA Identification in Mass Disasters

Answer 1)

Detection starts with evaluating the investigative information to understand the nature of the case and samples. Visual examination of stains with alternative light sources (such as ultraviolet or infrared light and lasers) and chemical enhancement reagents may be performed. Forensic biologists can determine the nature of the biological stain (for example, blood, semen, or saliva), and whether it is human through presumptive and confirmatory tests. These tests consist of analytical procedures including microscopy, chemical tests, and immunological assays (Nafte, 2000, 79).

DNA typing of STR polymorphisms is now widely used by law enforcement agencies and legal authorities to identify possible sources of forensic samples of human body fluids, and solid tissues as well. It has a well-established role in criminal investigations and prosecutions and has been effectively used to identify human remains from mass disasters. But problems surround its application to samples that contain DNA from two or more individuals and to badly degraded samples. Other forms of DNA typing, mitochondrial DNA typing for analysis of very badly degraded specimens and Y-STR typing identifying DNA from the male contributor to a mixed sample, are under development and may come to be useful if generally reliable techniques for typing and, more important, valid strategies for interpreting typing results can be developed.

DNA extraction

Following the detection and screening of samples from a crime scene, DNA must be extracted.

DNA quantification

Assessing the quantity and quality of the sample is the next step. Several methods are being utilized in crime laboratories. These include agarose gel electrophoresis in the presence of quantification standards (samples with known quantities of DNA), known as yield gel electrophoresis; slot blot hybridization, using known DNA standards immobilized on a membrane followed by hybridization to a human/higher primate-specific DNA probe; homogeneous plate assays, using a DNA fluorescent dye and scanning in a plate reader; and more recently, real-time detection using quantitative PCR (QPCR). Real-time QPCR has several advantages over the other methods in that it is extremely accurate and sensitive over a broad dynamic range, and it occurs in a closed-tube system, reducing the potential for carryover contamination. Using this technique, a forensic biologist can monitor and quantify the accumulation of PCR products during log phase amplification.

DNA amplification

PCR is a fast in-vitro DNA synthesis process that can provide up to a billion (109) copies of a given target sequence. Specific DNA markers can be targeted for duplication by a DNA polymerase. Primers are designed to hybridize to the specific markers along the length of the DNA template during the cycling of temperatures. In the thermal cycle, DNA strands are separated, primers bind to the template, and then a special DNA polymerase that is heat-stable is used to copy and amplify the genetic markers. Through a process of 28-32 heating and cooling cycles, the DNA is increased so that it can be analyzed. The thermal cyclers contain many sample wells, permitting the amplification of multiple samples simultaneously; as many as 96 ...