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DNA Fingerprinting

 DNA Fingerprinting 

     DNA profiling (also called DNA fingerprinting and genetic fingerprinting) is the process of determining an individual's deoxyribonucleic acid (DNA) characteristics. DNA analysis intended to identify a species, rather than an individual, is called DNA barcoding.

          DNA profiling is a forensic technique in criminal investigations, comparing criminal suspects' profiles to DNA evidence so as to assess the likelihood of their involvement in the crime. It is also used in paternity testing, to establish immigration eligibility, and in genealogical and medical research. DNA profiling has also been used in the study of animal and plant populations in the fields of zoology, botany, and agriculture.

          British geneticist Sir Alec Jeffreys independently developed a process for DNA profiling in 1984 while working in the Department of Genetics at the University of Leicester. Jeffreys discovered that a DNA examiner could establish patterns in unknown DNA. These patterns were a part of inherited traits that could be used to advance the field of relationship analysis. These discoveries led to the first use of DNA profiling in a criminal case.

          Although 99.9% of human DNA sequences are the same in every person, enough of the DNA is different that it is possible to distinguish one individual from another, unless they are monozygotic (identical) twins. DNA profiling uses repetitive sequences that are highly variable, called variable number tandem repeats (VNTRs), in particular short tandem repeats (STRs), also known as microsatellites, and minisatellites. VNTR loci are similar between closely related individuals, but are so variable that unrelated individuals are unlikely to have the same VNTRs.


Polymerase chain reaction (PCR) analysis


          This technique was developed in 1983 by Kary Mullis. PCR is now a common and important technique used in medical and biological research labs for a variety of applications.

          PCR, or Polymerase Chain Reaction, is a widely used molecular biology technique to amplify a specific DNA sequence.

Amplification is achieved by a series of three steps:


1- Denaturation : In this step, the DNA is heated to 95 °C to dissociate the hydrogen bonds between the complementary base pairs of the double-stranded DNA.


2-Annealing : During this stage the reaction is cooled to 50-65 °C . This enables the primers to attach to a specific location on the single -stranded template DNA by way of hydrogen bonding.


3-Extension : A thermostable DNA polymerase which is Taq polymerase is commonly used at this step. This is done at a temperature of 72 °C . DNA polymerase adds nucleotides in the 5'-3' direction and synthesizes the complementary strand of the DNA template .

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