FORENSIC MEDICINE

Following two techniques have been used in the area of forensic medicine to identify the culprits and criminals.

a) DNA fingerprinting using minisatellite DNA

The DNA fingerprinting method was developed by Alec Jeffreys and his colleagues in 1985-86. In this technique, DNA is isolated from the blood stains, semen or hair roots and then subjected to southern blotting and DNA hybridization with the help of specific DNA probes. The probes correspond to hypervariable minisatellites in DNA which in turn is made up of tandem repeats of short sequences.
This technique helps in the identification of criminals, rapists and accused using the blood stains, semen stains etc on the victim’s clothes or body. It will also help in solving the parental issues in case of doubtful parentage.

b) Autoantibody fingerprinting using dipsticks

Auto antibodies are a novel class of antibodies that react with cellular components in humans and other animal species. These human auto antibodies increase in number from birth up to the age of two years after which they remain constant for decades, if not life long. The complement of these antibodies present in an individual is unique and for this reason they have been named individual specific auto antibodies. These IS  auto antibodies  when physically separated comprise an antibody finger print that serves to identify people. For this also, body fluids such as blood, semen, tears, saliva and perspiration can be used.

The autoantibody fingerprinting protocol involves
a) preparation of antigen
b) antibody fingerprint assay

The protocol for autoantibody fingerprinting involves the following steps:

a) A panel of antigen is prepared from an extract of human cells in vitro which involves first the separation by denaturing polyacrylamide gel electrophoresis (SDS-PAGE) on the basis of molecular mass.

b) Electrophoretic transfer of the antigens to a nylon membrane.

c) Blocking of the unbound sites by using the blocking agents.

d) Cutting the membrane into strips called Dipsticks.

e) Incubation of the dipsticks with dilutions of sera or plasma for 1 hour.

f) After washing with buffer, incubate in detector molecule (1 micro-Ci/assay of 125 I protein, which binds to the Fc protein of human IgG in the immune complex formed) for 1 hour.

g) After re-washing and drying scan it with a gamma scanner or an optical scanner or perform autoradiography on X-ray film.

h) The results are analyzed for the identification of individuals.

Comparison of DNA fingerprinting and Autoantibody finger printing

The advantages of autoantibody fingerprinting over DNA fingerprinting include the following:

a) Sensitivity-less than 10 microl blood needed.

b) Rapidity-only few hours needed as time consuming method of DNA extraction is not required.

c) Simplicity-no requirement for any equipment.

d) Cost effectiveness

e) Portability

f) Autoantibody fingerprints are similar in the newborn child and the mother but are different in genetically identical individuals like identical twins. It is not possible to distinguish this using DNA fingerprinting.

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