Course: SAT 170 Introductory Biotechnology

Unit 14 Reading and Multimedia Assignment

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“Biotechnology used for genetic profiling and forensics” by Boundless, CC BY SA 3.0

https://www.boundless.com/biology/biotechnology/biotechnology-and-everyday-life/biotechnology-used-for-genetic-profiling-and-forensics/

Reading Assignment: Biotechnology used for genetic profiling and forensics
DNA profiling is a technique employed by forensic scientists to assist in the identification of individuals by their DNA makeup.

DNA Fingerprint

DNA profiling (also called DNA testing, DNA typing, or genetic fingerprinting) is a technique employed by forensic scientists to assist in the identification of individuals via their DNA profiles. DNA profiles are encrypted sets of numbers that reflect a person's DNA makeup. DNA profiling should not be confused with full genome sequencing. Profiling is used in parental testing and criminal investigation.

Although 99.9 percent of human DNA sequences are the same in every person, enough DNA is different to distinguish one individual from another—unless they are monozygotic twins. DNA profiling uses repetitive ("repeat") sequences that are highly variable, called variable number tandem repeats (VNTRs), particularly short tandem repeats (STRs). VNTR loci are very similar between closely related humans, but variable enough that unrelated individuals are extremely unlikely to have the same VNTRs.

Methods

The process begins with a sample of an individual's DNA (typically called a "reference sample"). The most desirable method of collecting a reference sample is the use of a buccal swab, as this reduces the possibility of contamination. When this is not available (a court order may be needed but unobtainable), other methods may be needed to collect a sample of blood, saliva, semen, or other appropriate fluid or tissue from personal items (e.g., toothbrush, razor, etc.) or from stored samples (e.g., banked sperm or biopsy tissue). Samples obtained from blood relatives (biological relatives) can provide an indication of an individual's profile, as could human remains that had been previously profiled. A reference sample is analyzed to create the individual's DNA profile using one of a number of techniques. The DNA profile is then compared against another sample to determine whether there is a genetic match.

The first methods for finding out genetics used for DNA profiling involved restriction enzyme digestion, followed by Southern blot analysis. Although polymorphisms can exist in the restriction enzyme cleavage sites, more commonly the enzymes and DNA probes were used to analyze VNTR loci. The Southern blot technique is laborious and requires large amounts of undegraded sample DNA. In addition, Karl Brown's original technique looked at many minisatellite loci at the same time, increasing the observed variability but making it hard to discern individual alleles (and thereby precluding parental testing). These early techniques have been supplanted by PCR-based assays.

With the invention of the polymerase chain reaction (PCR) technique, DNA profiling took huge strides forward in both discriminating power and the ability to recover information from very small (or degraded) starting samples. PCR greatly amplifies the amounts of a specific region of DNA, using oligonucleotide primers and a thermostable DNA polymerase.

Criminal Investigation

One of the most well known applications of DNA profiling is in the use of criminal investigation. DNA evidence can be collected at a crime scene in the form of hair, skin, blood, or other bodily fluids. These samples can be compared to those of various suspects to identify a match. Although used in less than one percent of all criminal cases, DNA profiling has helped to acquit or convict suspects in many of the most violent crimes, including rape and murder. Because DNA evidence is so specific, it is actually much easier to exclude a suspect than to convict someone based on a DNA match.

Identifying the victims of the September 11, 2001, World Trade Center attack presented a unique forensic challenge because the number and identity of the victims were unknown and many victims were represented only by bone and tissue fragments. At the time of the attack, no systems were in place to rapidly identify victims in disasters with more than 500 fatalities. The National Institutes of Justice assembled a panel of experts from the National Institutes of Health and other institutions to develop processes to identify victims using DNA collected at the site. Panel members produced forms and kits that enabled the medical examiner’s office to collect reference DNA from victims’ previously stored medical specimens. These specimens were collected and entered into a database.