DNA FINGERPRINTING

 

What is DNA fingerprinting?

 

Alec Jeffreys

DNA fingerprinting is a technique to identify a person based on his/her DNA specificity. Every individual organism is unique. Thus every person has unique DNA fingerprint. It can't change by any known technique. It is a quick way to compare the DNA sequences of any two individuals. DNA fingerprinting developed by Alec Jeffreys.

 

 

Paternity test

Applications:

 

1. Paternity test
2. Criminal Identification
3. Determination of population diversity
4. Determination of genetic diversity
   

 

Principle:

It has found that the DNA of an individual carries some specific nucleotide sequences which don't code for any information or proteins. These sequences repeated many times and found at many places throughout the DNA. These sequences of satellite DNA which are very specific in each individual and vary in number from person to person and are inherited. These are a variable number of tandem repeats (VNTRs). Each individual inherits these repeats from his/her parents which used as genetic markers in personally identifying test. Half of the VNTRs of the child resembles that of the mother and half that of the father. 

Steps:

  

1.Isolation of DNA- 

The DNA is extracted from the nuclei of WBC or of spermatozoa or from the follicle cell.

  

2. Fragmentation of DNA-

Gel-electrophorosis

The DNA molecule first cut with the help of enzyme restriction endonucleases that cuts them into fragments. These fragments of DNA contains VNTRs.

  

3.These DNA fragments are separated according to size by the Gel-electrophoresis.

 

4.These separated DNA fragments in the gel copied onto the nylon membrane by Southern Blotting Technique.

  

5.Hybridization-

• Special DNA probes are made in the lab. These DNA probes contain the repeated sequence of the base containing VNTRs.
• These probes are made radioactive by labelling with radioactive isotopes.
• The radioactive DNA probes bind to the repeated DNA sequences on the nylon membrane. This is called Hybridization.

DNA fingerprint

 6.Autoradiography-

• X-ray film is exposed to the nylon membrane to mark the places, the radioactive DNA probes have bound to the DNA fragments.
• These places are marked as dark bands when x-ray film is developing. This is known as autoradiography.
• Those dark bands on the x-ray film represent the DNA fingerprints.