“Proteins and DNA are used as Evidence as Legal Proceedings”

In the past, fingerprints were used for protecting the immigration laws worldwide; to track down those living in countries they illegally belonged to. However, after several years, two scientists from England, United Kingdom discovered fingerprinting to be of a better use. The fingerprints eventually used to identify or exonerate suspects in criminal investigations. Criminal investigators also use DNA and protein profiles to catch their criminals. Although fingerprints can be used, they are very unique to discover, causing them to be rarely perfect and not always available as many criminals use gloves to avoid leaving their fingerprints.
Another method used to track criminals is using ones’ blood. This is because each individual has one of the four types of blood available, group O, A, B or AB. So, if someone’s blood is found, the investigators can narrow down the suspects as only a certain percent of people have the particular blood group. For example in the United States of America only, 42% have the blood type A, 12% have the blood type B 43% have the blood type O and only 3% have the blood type AB.1 As a result, the disadvantage of this method is that they do not narrow down the results to an individual suspect, it just connects several people to the crime, whether they are guilty or not. The other method of using protein profiles to track down criminals is based on the presence or absence of certain cell membrane proteins. However, it has the same disadvantages regarding to blood samples. It only narrows down the results to several people rather than giving the results of one individual suspect. Although the protein profiles and blood are generally found to be useful and helpful to analyze, especially as only small amounts are needed, they degrade very quickly and, consequently, can only be used when the DNA or protein profiles are found fresh as it gives accurate results.
DNA can be extracted from very small biological samples such as from hair, blood, semen, saliva residues on envelopes and cigarette butts and also from cells from fingernail scrapings. These DNA samples and results can be used to compare the results of the suspects and compare the similarities and differences of the results. This allows an investigator to exempt individuals who are innocent and allow them to analyze suspects whose results have a similar DNA to the ones they found. This can be done because each individual (apart from identical twins) have their own distinctive set of DNA, enabling the forensic science department to be extremely certain about the concluded results.
When the DNA is collected from the crime scene, the DNA is copied, using a technique called a polymerase chain reaction. A large fraction of DNA contains sequences of bases that are repeated over and over again, up to 30 times in a row, which have no known function. The lengths of most of these repetitive segments vary significantly between individuals which allow forensic scientists to distinguish one individual from another. 1 The long strands of DNA are cut into pieces with the help of restriction enzymes. The fragments are sorted out by length using electrical charges. Further treatment and transfer of the separated fragments to a nylon membrane produces a series of bands called a DNA fingerprint that is unique to each individual. This allows criminal investigators to directly compare two or more individuals DNA to see if they match or not.
Although the DNA found in the nucleus of cells are commonly used, the DNA found outside the nucleus, the mitochondrial DNA, is also used and has been said to be more beneficial than regular DNA. Mitochondria DNA can be found in ones’ hair or bones in dead remains. It is more beneficial because the DNA is derived from the mother alone which has a high rate of mutation than nuclear DNA. Therefore, it is useful in discovering the evolutional history of individual species.
One of the controversial issues within forensic science is whether the forensic or criminal department should be able to force criminals to submit samples of the DNA for testing and also to keep for records. Should they be able to keep your genetic information even if they do not use it?
I think that it is very clever how they use DNA to track down criminals. Not only that but they can extract the DNA from very small samples, including hair. Technology nowadays is becoming very advance allowing investigators to find their job very easy to catch the criminals.


Deoxyribonucleic Acid (DNA) – a polymer of nucleotide subunits in which the sugar is deoxyribose.

Protein – polyamides formed from α-amino acids, which are the most important constituent of living things.

Polymerase Chain Reaction – a process that copies a small segment of DNA, millions of times, to obtain a sample large enough for analysis.

Restriction enzymes – special molecules that seek out specific base sequence on DNA.

Mitochondria DNA – DNA found outside the nucleus.



1 Braid. Chemistry in Your Life. 2nd ed. New York, USA: W.H.Freeman and Company; 2006. pp 358-360.