Question

Briefly explain how repetitive DNA is useful for identifying individuals by the techniques of DNA fingerprinting.

Answer 1

DNA fingerprinting is a laboratory method used to identify an individual or even organisms using their DNA samples. DNA fingerprinting makes use of the repetitive part of the DNA in this process.Only 3% of DNA are genes which encodes proteins while rest 97% accounts for the non-coding, repetitive and junk DNA. In different organisms, the junk region of DNA is highly repetitively polymorphic in nature. This means the number and nature of repetitive DNA vary among individuals. This property is utilised in DNA fingerprinting techniques.Junk or non-coding repetitive DNA doesn't code for any protein, instead it helps in regulating gene expression. There are two types of tandem repeats Variable number of tandem repeats (VNTR) and Short tandem repeats (STR). Tandem repeats are those patterns of one or more nucleotides repeated directly adjacent to each other. Satellites DNA are those repetitive non-coding DNA regions located on telomeres and centromeres which help chromosomes prevent replication error.VNTR is a type of Minisatellite region (repeated DNA sequences of 10 to 60 bp). Usually 5-50 repeats of this is found in human genome.STR is an example of Microsatellite region ( usually 1-6 bp long and repeated 5 to 10 times.in the human genome).The possibility of having the same number of repeats and corresponding base pair number for these VNTRs and STRs for different individuals is almost negligible unless they are monozygotic twins(still there would be small differences). A restriction endonuclease can digest one particular VNTR region of different individuals and this when passed through Agarose gel electrophoresis or DNA sequencing shows different patterns for different individuals.The similarity in the resultant band patterns shows the closeness or relations of the individuals tested. According to studies, the chance of two individuals possessing the same DNA profile is 1 in 10,000,000,000,000 while the total world population is 7,600,000,000. Thus the probability. And thus repetitive DNA is useful for identifying individuals by the techniques of DNA fingerprinting.