Sir Alec Jeffreys

DISCOVERY OF THE DNA FINGERPRINT

It was not until 20 years ago that Sir Alec Jeffreys, professor and geneticist at the University of Leicester in the United Kingdom (UK), pioneered DNA-based identity testing.

What is the definition of DNA fingerprinting?

DNA fingerprinting is a laboratory technique used to establish a link between biological evidence and a suspect in a criminal investigation. A DNA sample taken from a crime scene is compared with a DNA sample from a suspect.

The Steps of DNA Fingerprinting
DNA fingerprinting involves a number of intensive and important steps in order to fully complete and develop and DNA fingerprint of a father, a suspect or a person involved in an immigration problem.

1.The process of DNA fingerprinting starts with isolating DNA from any part of the body such as blood, semen, vaginal fluids, hair roots, teeth, bones, etc.

2.Polymerase chain reaction (PCR) is the next step in the process. In many situations, there is only a small amount of DNA available for DNA fingerprinting. Because of this, in a test tube, DNA replication is must occur to make more DNA. The DNA and the cells will undergo DNA replication in order to make more DNA to be tested.

After the DNA is isolated and more copies of the DNA have been made, the DNA will be tested. The scientist will treat DNA with restriction enzymes (an enzymes that cuts DNA near specific recognition nucleotide sequences known as restriction sites).

This will produce different sized fragments which are known as restriction fragment length polymorphisms (RFLPs).
- These fragments can then be observed doing an experiment called gel electrophoresis which separates DNA based on fragment sizes.

4.Gel electrophoresis is the next step in this process of DNA fingerprinting. During gel electrophoresis, an electrical current is applied to a gel mixture, which includes the samples of the DNA.
-The electric current causes the DNA strands to move through the gel. This separates the molecules of different sizes.
-The fragments of separated DNA are sieved out of the gel using a nylon membrane (treated with chemicals that allow for it to break the hydrogen bonds of DNA so there are sing strands).

5.The DNA (single stranded) is cross-linked against the nylon using heat or a UV light.

6.The probe shows up on photographic film because the strands of DNA decay and give off light. In the end it leaves dark spots on the film which are also known as the DNA bands of a person. What make up the fingerprint are the unique patterns of bands. The pattern of bands are different because we are all different and unique (other than identical twins).

Forensic Science:

1.Biological materials used for DNA profiling are: Blood, Hair, Saliva, Semen, Body tissue cells etc. DNA isolated from the evidence sample can be compared through VNTR (Variable number of tandem repeats) prototype. It is useful in solving crimes like murder and rape.

2.Paternity and Maternity Determination:

u A Person accedes to his or her VNTRs from his or her parents. Parent-child VNTR prototype analysis has been used to solve disputed cases. This information can also be used in inheritance cases, immigration cases.

3.Personal Identification:

It utilizes the concept of using DNA fingerprints as a sort of genetic bar code to pinpoint individuals.

DNA Ligation

Plasmid isolation

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