DNA fingerprinting is a laboratory technique for determining a person's likely identity based on the nucleotide sequences of specific regions of human DNA that are unique to individuals.

1. DNA FINGERPRINTING
DNA fingerprinting is a laboratory
technique used to establish a link between
biological evidence and a suspect in a criminal
investigation. A DNA sample taken from a crime
scene is compared with a DNA sample from a
suspect. If the two DNA profiles are a match,
then the evidence came from that suspect.
Conversely, if the two DNA profiles do not
match, then the evidence cannot have come from
the suspect. DNA fingerprinting is also used to
establish paternity.
RITHIKA. R. S,
I - M. Sc. Bioinformatics,
Sri Krishna Arts and Science College, Coimbatore.
DNA FINGERPRINTING
The area with same sequence of bases
repeated several times in DNA is called repetitive
DNA. They can be separated as satellite from the
bulk DNA during density gradient centrifugation
and hence called satellite DNA. In satellite DNA,
repetition of bases is in tandem. Depending upon
length, base composition and numbers of tandem
repetitive units, satellite DNAs have
subcategories like microsatellites and mini-
satellites. Satellite DNAs show polymorphism.
Mutations in the noncoding sequences have piled
up with time and form the basis of DNA
polymorphism. DNA polymorphism is the basis
of genetic mapping of human genome as well as
DNA finger printing. Short nucleotide repeats in
the DNA are very specific in each individual and
vary in number from person to person but are
inherited. These are the ‘Variable Number
Tandem Repeats’ (VNTRs).
PRINCIPLE
Each individual inherits these repeats from his/her
parents which are used as genetic markers in a personal
identity test.
1. 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.
2. The DNA molecules are first broken with the help
of enzyme restriction endonuclease. The fragments
of DNA also contain the VNTRs.
3. The fragments are separated according to size by
gel electrophoresis.
4. 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.
5. The separated fragments of single stranded DNA
are transferred onto a nylon membrane.
6. 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 nylon
membrane is washed to remove extra probes.
7. 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.
8. The dark bands on X-ray film represent the DNA
fingerprints(DNA profiles).
TECHNIQUES
Methods involved
DNA profile