Question

Two blood samples A and B picked up from the crime scene were handed over to the forensic department for genetic fingerprinting. Describe how the technique of genetic fingerprinting is carried out. How will it be confirmed whether the samples belonged to the same individual or to two different individuals?

Answer 1

DNA Fingerprinting: This technique was discovered by Alec Jeffreys in 1985. 

The technique involves following steps: 

(i) Isolation and extraction of DNA from the cell by centrifugation. 

(ii) By the help of enzyme restriction endonuclease, DNA molecules are digested. The fragment also contains VNTRs. 

(iii) The small DNA fragments are separated through gel electrophoresis set-up that contain agarose polymer gel. 

(iv) The separated DNA fragments are transferred from electrophoresis plate to synthetic membranes like nitrocellulose or nylon membrane sheet called Southern blotting. 

(v) The DNA probes are added which target a specific nucleotide sequence which is complementary to them and this process is called hybridisation. 

(vi) The nylon membrane is exposed to an X-ray film and dark orange coloured bands developed at sites where probes have bound to the DNA fragments. This is known as autoradiography. 

On comparing the DNA prints of blood samples A and B, it can be confirmed that the blood sample picked up from the crime scene belongs to the same individual or to two different individuals.