DNA fingerprinting
- The process of comparison of DNA from different sources to establish the identity is called DNA fingerprinting.
- 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.
- 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, 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.
- 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.
DNA fingerprinting in identification of criminals
