2. • DNA profiling is the process of determining an individual's DNA characteristics.
• 99.9 per cent of base sequence among humans is the same
• DNA profiling is the process of determining an individual's DNA characteristics.
DNA fingerprinting technique is developed by Alec Jeffrey (1978)
Basis of DNA Fingerprinting
• DNA polymorphisms: Different DNA sequences
among individuals, groups, or populations.
• Polymorphism at the DNA level includes a wide
range of variations from single base pair change,
many base pairs, and repeated sequences
• Single Nucleotide Polymorphisms: SNP is a single base pair change, a point mutation,
and the site is referred to as SNP locus
• RFLP- Restriction Fragment length Polymorphisms
• Short Tandem Repeats
• VNTRs - Variable Number Tandem Repeats
• Microsatellite Markers
3. • DNA fingerprinting involves identifying differences in some specific regions in DNA
sequence called as repetitive DNA.
• Because in these sequences, a small stretch of DNA is repeated many times.
Satellite DNA
• Satellite DNA are DNA sequences that contain highly repetitive DNA.
• Highly repetitive DNA consisting of short sequences repeated a large number of
times.
• It carries a variable AT-rich repeat unit that often forms arrays up to 100 Mb.
• Repetitive DNA are separated from bulk genomic DNA as different peaks during
density gradient centrifugation.
• The bulk DNA forms a major peak and the other small peaks are referred to as
satellite DNA.
A- Micro-satellites
B- Mini-satellites
DNA sequences that contain small segments, which are repeated many times.
Repetitive DNA
4. •
Minisatellite and Microsatellite
Minisatellite Microsatellite
It has repeating units of 25 bp 13 bp
Distributed towards telomeric sites Throughout chromosome
Difficult in handeling (base pairs are in kilo) Easy in handeling (base pairs are in hundreds)
Not used frequently Used frequently
• These sequences normally do not code for any proteins, but they form a large portion of human
genome.
• These sequence show high degree of polymorphism and form the basis of DNA fingerprinting.
• The probability of such variation to be observed in noncoding DNA sequence would be higher as
mutations in these sequences may not have any immediate impact in an individual’s reproductive
ability.
• These mutations keep on accumulating generation after generation, and form one of the basis of
variability/polymorphism.
5. (VNTR)
• Alec Jeffreys used a satellite DNA as probe that shows very high degree of polymorphism.
It was called as Variable Number of Tandem Repeats (VNTR)
• The VNTR belongs to mini-satellite.
• size of VNTR varies in size from 0.1 to 20 kb.
6. STEPS IN DNA FINGERPRINTING
(i) isolation of DNA
(ii) digestion of DNA by restriction endonucleases
(iii) separation of DNA fragments by electrophoresis
(iv) transferring (blotting) of separated DNA fragments to synthetic membranes, such as
nitrocellulose or nylon
(v) hybridisation using labelled VNTR probe
(vi) detection of hybridised DNA fragments by autoradiography.
