DNA finger printing or DNA profiling

DNA finger printing or DNA profiling is a technique of DNA diagnosis in which images of the DNA band is recorded on an X-ray film. This method was developed by Alec Jeffreys in 1984.

Methodology:

DNA fingerginting is based the sequence polymorphism that occurs in the the genome of every organisms. The sequence polymorphism are slight sequence differences ually single base pair changes, that occur from individuals to individuals once every few hundred base pairs on average. Each difference from the consensus genome sequence is generally present in only a fraction of the population but every individual has some of them. These polymorphic loci are called minisatellite or VNTR (variable number tandem repeat). Thus VNTR serve as a marker key for identification in DNA finger printing.

1. Isolation of Cell DNA:

DNA is isolated from the source material and the suspected individuals. Any biological materials such as drop of saliva, semen, teeth bones, tissues, roots etc are used to isolate DNA.

2. Restriction Digestion:

The cell DNAs are separately cut with a restriction enzyme to generate short fragments

3.PCR Amplification:

Since samples provide a small amount of DNA, PCR is performed in a PCR machine to get several copies of DNA for DNA ﬁngerprinting

4. Gel Electrophoresis:

The DNA restriction diest of the source material, are poured into separate wells of an electrophoresis gel and electrophoresed. The minisatellites separate according to their lengths.

5. Southern Blotting:

The separated DNA fragments are transferred to a nylon membrane or a nitrocellulose ﬁlter paper by placing it over the gel. This process is called southern blotting.

6.Baking:

The nitrocellulose ﬁlter having DNA fragments is dried in between dry ﬁlter papers at high temperature. This process is called baking.

7. Selection of DNA Probe:

In the USA, DNA probes constructed by Alec Jeﬂreys, are used for DNA ﬁngerprinting. However, these probes are not available to India. Dr. Lalji Singh at the Centre for Cellular and Molecular Biology in Hydrabad, has developed a DNA probe from minisatellite DNA of banded krait (Bungarus fasciatus) an Indian poisonous snake and named it BKm probe. The BKm probe is being used for DNA ﬁngerprinting in India.

8. Filter Hybridization:

The nitrocellulose ﬁlter is placed in an alkali solution to denature the duplex DNA fragments.Then it is placed in the hybridization solution containing the probe DNA. The probe DNA binds with appropriate minisatellites and forms duplex DNAs. 8. Autoradiography:After hybridization, the ﬁlter is washed with a wash solution to remove unbound probes. Then an X-ray film is placed over the ﬁlter for about 3 hours.The radioactivity of the probes makes dark spots on the X-ray ﬁlm. Therefore, an irregular ladder of dark spots develops on the X-ray ﬁlm, for each and every DNA sample. Each ladder represents a DNA print of an individual. All DNA prints on the X-ray ﬁlm together constitute a DNA ﬁngerprint pattern.

9.Analysis of DNA finger printing pattern:

DNA ﬁngerprint pattern is then analysed for determination of similarity or dissimilarity of two individual or to establish the genetic relationship.

Application of DNA ﬁngerprinting:

DNA finger printing technology has applications in many areas….

(i)Setting up of genetic Data base:

Realising the potential of DNA finger printing the genetic data bank had been set up throught the world.Data bases of the genetic finger prints of criminals have been set up in many parts of the world.

(ii)Settle down the parental disputed problem:

In some abnormal cases, court cannot decide who is the real parent of a child.By analyzing the DNA ﬁngerprint pattern of parent and child, the problem can be settle down easily.

(iii)To settle criminal cases:

DNA ﬁngerprinting helps the police and court to settle some criminal offence like murder or rape.It is simply done by analysis of DNA fingerprint pattern of suspects DNAs and DNA isolated from the criminal tissue found on victim’s body.

(iv)Pedigree analysis:

DNA finger printing is used in pedigree analysis in Cat,Dog,Horses,Plants and Human.

(v)Migration pattern:

It is also used to assess the pattern of migration of ancient population.

(vi)Immigrant dispute:

More or less in every country, there is a problem of immigration. Ultimately the identity is not confirmed whether they have crossed the borders or ae the resident of the country.Therefore the problem of immigrant can be solved by this technique. (vii)Genetic analysis:It is also employed in genetic analysis of various strains of agricultural crops and animals.