Before DNA technique discovery it was possible to identify people in other different ways using finger-printing since 1901, other observations led to find different types of particular proteins that could be present or absent.
How?  Evidence were compared with suspect 's pattern but the result of this investigation could be only used to exclude from a crime and not to accuse anybody.  

DNA finger printing was used since 1984. It was developed by Alec. J.Jeffreys,  a molecular geneticist at the University of Leicester, Uk.  It was used for the first time in 1986 during a case of  two teenage girls's  murderer in England. 

DNA can be obtained from biological materials like blood, semen, hair with roots, skin, dandruff, sweat stains, vaginal fluids, nasal secretions, urine, feces. 

RFLP ( Restriction Fragments Lenghts Polymorphism ) technique was invented by Alec J. Jeffreys in 1984. 

 Their action mechanism provides to cut in pieces double strand viral DNA injected by viral particles. They are classified as endonucleases, we know about three thousand different types of restriction enzymes. 

 Restriction enzymes have been developed inside bacteria cytoplasm to prevent viral o bacteriophage infection.

 The electrophoresis principle is based on different speed rates of different size fragments towards anode. As agarose gel is like a filter, the shortest fragments will run quickly instead the longest ones will be slowed down and we can see them nearer the well. Shorter DNA fragments travel through the gel faster than a sample with larger fragments. 

DNA migrates toward positive electrode because it has a negative charge. 

 The experimental conditions for digestion are defined at 37°C, pH controlled by TBE buffer solution, presence of Mg ions, Na Cl for the proper ionic strength (i). 

Add Mg ions is important to focus activity on enzymes. They are co-enzymes.

 Gel Electrophoresis the gel sheet is laying inside the gel tray. There are wells where DNA extracts are carefully loaded. TBE solution soaked into the gel. Applying the right voltage negatively charged DNA fragments will travel through the gel sheet towards positively charged electrode. 

DNA dye are dangerous for human health because it can produce carcinogenic effects.  

At first, mix up agarose powder with buffer solution. Then heat the mixture in microwave a wide container. Mix solution during heating to full dissolve the agarose. When we preparing agarose is should be better wear gloves because some substances could be dangerous. 

Over the container the cover must not be loose, this is to prevent the solution from splashing out. The solutions should not be partially dissolve but should be full dissolved otherwise the result will not be accurate.

 We will see a fragment pattern: the sample with the same pattern found in the crime scene is the culprit. 

DNA has received a lot of media attention because it has a fantastic power of discrimination. It is a strong evidence more than eyewitness and it allows to compare billions or trillions DNA's profile. 

DNA has been used to identify people since mid-eighties but during the years the technical is improved. 

Nowadays is enough less than an anagram (WW nanogram) of DNA instead 50  nanograms or a microgram of DNA in the past. 

Three or four cells of the property are needed to get a full profile. 

The exhibit be kept in bone dry conditions and if it's possible you can freeze it in a piece of  tissue. 

DNA taken in good conditions will last essentially forever.  

 

Observation: DNA finger printing was used since 1984. It was developed by Alec. J.Jeffreys,  a molecular geneticist at the University of Leicester, Uk.  It was used for the first time in 1986 during a case of  two teenage girls's  murderer in England.  Nowadays this technical is very improved, it allows to compare billions or trillions DNA's profile and it is enough less than an anagram of DNA to identify a person. DNA finger printing is used to identify people but also for paternity test. At the end of the experiment we could identify the culprit comparing the DNA fragments of the samples with DNA of the crime scene. During the experiment you must be pay attention using DNA dye because it is dangerous for human health, it has carcinogenic effects.