DNA Fingerprinting Technique - Polymorphism

Polymorphism:

• Polymorphism is the variation at the genetic level.
• It arises in an individual either in somatic cells or in the germ cells.
• Mutations are inheritable (Unless the mutation in the germ cell hampers the ability of an individual to produce offsprings). 
• If more than one variant (allele) occurs at a locus with a frequency of more than 0.01, then the allelic sequence variation is known as 'DNA polymorphism'. Thus, any inheritable mutation which is observed at high frequency in a population is referred to as 'DNA polymorphism'. 
• Variations are majorly observed in non-coding DNA sequences (they do not have any immediate effect on individual).  
• Polymorphism ranges from single to large scale changes, both of which play important role in evolution and speciation.  
• Dr. Alec Jeffreys developed the technique of DNA fingerprinting in an attempt to identify DNA markers for inherited diseases.  
• He used satellite DNA as probe that shows a very high degree of polymorphism. It was called Variable Number of Tandem Repeats (VNTR) or mini-satellite. 
• A technique to identify a person on the basis of a person's DNA specificity is called DNA fingerprinting.
  

Variable Number of Tandem Repeats (VNTR): 

• VNTRs are also known as minisatellites and are made up of tandem repeats of short base sequences (10-100 base pairs).  
• It is a small sequence of DNA present one behind other (tandemly) in variable numbers.
• High degree of variation is seen in the number of repeats. 
• Size of VNTR varies from 0.1 to 20 kb. Copy number varies from chromosome to chromosome in an individual. 
• The autoradiogram obtained after hybridization with VNTR probe produces bands of differing sizes. These bands are characteristic for an individual. 
• Except monozygotic twins, no two individuals have same autoradiogram pattern.  
• By use of polymerase chain reaction and different probes, the sensitivity of DNA fingerprinting can be increased.