MOLECULAR BIOLOGY 14

 DNA fingerprinting

• The process of comparison of DNA from different sources to establish the identity is called DNA fingerprinting.

All persons 99.9% DNA same

0.1 % different and unique to individual - this is used in DNA fingerprinting.

Whole DNA sequence for differentiating 2 DNA would be very hectic.

• DNA fingerprinting involves identifying differences in some specific regions in DNA sequence called as repetitive DNA.

• 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.
• Means - satellite DNA contains - repetitive DNA

• Satellite DNA is of two types based on base composition, length of segment, and number of repetitive units
• micro-satellites
• mini-satellites

Satellite DNA

• Satellite DNA sequences normally do not code for any proteins, but they form a large portion of human genome.

• Satellite DNA sequence show high degree of polymorphism and form the basis of DNA fingerprinting.

• An inheritable mutation occurring in a population at high frequency, (more than 0.01- 1%) is referred to as DNA polymorphism.

• Repeated nucleotide sequences in the non-coding DNA of an individual is called Variable Number of Tandem Repeats (VNTR).

• The size of VNTR varies in size from 0.1 to 20 kb. (Kilo base pairs)

• DNA fingerprinting includes the following steps
• isolation of DNA
• digestion of DNA by restriction endonucleases
• separation of DNA fragments by electrophoresis
• transferring (blotting) of separated DNA fragments to synthetic membranes, such as nitrocellulose or nylon.
• hybridization using labelled VNTR probe
• detection of hybridized DNA fragments by autoradiography.

Fragments of DNA

Applications

• In identification of criminals.
• In determining population and genetic diversities.
• In solving parental disputes