What is DNA?
DNA (noun) deoxyribonucleic acid
First appeared 1944 : any of various nucleic acids that are usually the molecular basis of heredity, are localized especially in cell nuclei, and are constructed of a double helix held together by hydrogen bonds between purine and pyrimidine bases which project inward from two chains containing alternate links of deoxyribose and phosphate.
What is forensics?
fo*ren*sic 1 (adjective)
First appeared 1659
1 : belonging to, used in, or suitable to courts of judicature or to public discussion and debate.
2 : ARGUMENTATIVE, RHETORICAL.
3 : relating to or dealing with the application of scientific knowledge to legal problems * medicine* * science* * pathologist* * experts*.1
How are the two related?
DNA can be used to identify an individual. In relation to forensics, when there is a crime investigation and some proof is needed to back up the suspect DNA is usually the way that scientist deal with the situation. Specialized forensic scientists scan about ten DNA regions that vary from person to person and use the data to create a DNA profile for that individual. This is effective because there is a very small chance that another individual has the same DNA profile in the same set of regions.
DNA can be used for many other things besides for committing a suspect. It can also free a person wrongly accused of a crime, identify crime and catastrophe victims ,establish paternity and other family relationships ,detect bacteria and other organisms that may pollute air, water, soil, and food ,and even match organ donors with recipients in transplant programs .
How effective is DNA in identifying a person?
DNA identification must be used intelligently. When you find a certain thing through DNA at a crime scene that thing alone may not be enough. However if many little things are found then you can connect them all and find what you need. If the first thing you find is found in almost half of the American population that is not very helpful but if you keep on finding more and more things eventually it is narrowed down to one specific person.
Once the DNA is found how is it typed up?
Only one-tenth of a single percent of DNA makes one person different from the next. Scientists can use these variable regions to create a DNA profile for a person, using samples from hair, blood, bone and other body tissues and products. Generally in criminal cases this involves getting samples from crime-scene evidence and a suspect giving off some DNA, and analyzing it for the presence of a set of specific DNA regions.
Scientists find the markers in a DNA sample by designing small pieces of DNA called probes that will each seek out and tie to a complementary DNA sequence in the sample. A series of probes tied to a DNA sample creates a unique pattern for an individual. Forensic scientists compare these DNA profiles to the suspect’s sample to see if the suspects sample matches the evidence sample. If two samples are alike at four or five regions, most probably the suspect contributed his DNA to the crime-scene evidence, though there is a slim chance that someone else has the same DNA profile for a particular probe set.
The question is how small of a chance must there be when convicting the guilty or the vindication of the innocent lies in the balance? The judges often let the jury decode based on this and other evidence involved in the case. Experts say that using DNA forensic technology is better then eyewitness accounts.
Sources of DNA for testing
Once bloodstains are found an analysis can most probably be made. But it depends on the surface or substrate on which it is found. If the blood is found on glass, metal, hard plastics or lightweight cloth it is easy to extract the blood and analyze it. If found on other dense and heavily colored fibers a few additional steps are required. Soil and concrete are almost impossible substances and surfaces because it is so hard to extract the blood from them. From the blood it can be figured out if the bloodstain is from a male or female. It can also tell us how many people it involved for a DNA profile of two people is far more complex then a DNA profile for one person. Specimens that are drawn from the victims or suspects are called known exemplars. They usually consist of liquid blood. The best storage for blood is frozen. Buccal or the inside of your cheek can also be supplied as exemplars. For people who cannot have blood drawn for any particular reason it is used instead of blood.
Semen- Semen stains are the most common evidence to be submitted for DNA analysis. Sperm cells and non-sperm cells can, as well as blood, be separated.
Isolation of DNA from tissues is a simple straightforward process. Usually, soft tissues received in the laboratory are from partially decomposed bodies. DNA last shorter in liver and kidney, longer in muscle and brain and even longer in dense bone and teeth. Sometimes DNA can be drawn from a bullet or weapon used to injure the brain or any other tissue. If a body is not recovered and only bits of tissue are then they can be used and compared with surviving family members.
Chemically Treated Tissues-
There are two common chemical treatments, formaldehyde for medical purposes and embalming. DNA can be drawn from both tissues. Even bodies that have been buried for several years can give results.
The sufficient amount of hair needed for analysis is one to five hair roots. Shed hairs contain only traces of DNA and are generally not suitable for testing in forensic use. A highly specialized method known as mitochondrial sequencing is starting to be used more and more.
DNA can be taken from saliva deposited on almost everything. Envelope flaps or stamps, as was done in the New York World Trade Center bombings. It can also be drawn from cigarette butts, cups, bottles, telephone mouthpieces and bite marks found at crime scenes.
DNA sampling from urine is not very common. Since healthy individuals do not shed nucleated cells into urine. Conventional testing is more likely to give results and is used to test for drug use.
Products of Conception-
When a teenaged girl has been impregnated by a relative or other adults the non-living product must be analyzed. As well as in a rape or anything resulting in pregnancy.
How did the forensic use of DNA start?
Alec Jeffreys , a geneticist at the University of Leicester in Britains Midlands,
started forensic use of DNA. He invented the techniques that took human identification from the laboratory to the courtroom in 1984. He called the process “DNA fingerprinting” which is not used by most forensic scientists because it can be misleading. He applied his techniques to an immigration case. A boy from Ghana wanted to emigrate to Britain, claiming his mother was already a resident. A DNA analysis showed that the two were in fact related and the Home Office put its stamp of approval on the new technology.