Two blood samples A and B picked up from the crime scene were handed over to the forensic department for genetic finger printing. Describe how the technique of genetic finger printing is carried out.

Explanation

Technique For DNA Fingerprinting. The DNA is extracted from the nuclei of white blood cells or of spermatozoa or of the hair follicle cells that cling to the roots of hairs that have fallen, or been pulled out.(ii) The DNA molecules are first broken with the help of enzyme restriction endonuclease (called chemical knife) that cuts them into fragments. The fragments of DNA also contain the VNTRS The fragments are separated according to size by gel electrophoresis.
(iv) Fragments of a particular size having VNTRs are multiplied through PCR technique. They are treated with alkaline chemicals to split them into single stranded DNAS
(v) The separated fragments of single stranded DNA are transfered onto a nylon membrane
(vi) Radioactive DNA probes having repeated base sequences complementary to possible VNTRs are poured over the nylon membrane. Some of them will bind to the single stranded VNTRs. The method of hybridization of DNA with probes is called Southern Blotting, after the name of the inventor, E.M. Southern (1975). The nylon membrane is washed to remove extra probes.
(vii) An X-ray film is exposed to the nylon membrane to mark the places where the radioactive DNA probes have bound to the DNA fragments These places are marked as dark bands when X-ray film is developed. This is known as autoradiography.
(viii) The dark bands on X-ray film represent the DNA fingerprints (= DNA profiles).