DNA Fingerprinting

    What is a DNA Fingerprinting?

    It is a molecular technique that is used to collect genetic information about the person to assist in the parentage testing, criminal and forensic investigations. DNA fingerprinting history started in 1984 with the discovery of minisatellite DNA by Alec Jeffrey. He realised that highly variable sequences of minisatellite DNA can be used for personal identification. Those sequences create a unique pattern – DNA fingerprint that differs even among close relatives with the exception of identical twins. In order to perform fingerprint analysis, researchers need a biological sample. It can be buccal swab, hair, saliva or blood sample or any other tissue available.

    What methods are used for genetic fingerprinting?

    There are several methods for DNA fingerprint analysis.

    RFLP (restriction fragment length polymorphism) analysis is the oldest and the most time-consuming method, which provides excellent results, but cannot be used for parentage testing. The essence of this method is in cutting DNA in pieces using the restriction enzymes. All the variety of DNA pieces then separated by size on the gel. Electric current that run through the gel make DNA move. The larger fragments move slower in the gel than smaller ones, thus creating a ladder of separated fragments. Those fragments are later transferred to the nylon sheet where only minisatellite DNA bonds to radioactive markers. Marked fragments are the DNA fingerprints, which can be further analysed.

    Advancement in the technology facilitated DNA fingerprinting analysis. The invention of PCR (polymerase chain reaction) increased the speed of the DNA fingerprinting process. This method in contrast with RFLP 

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    can use subtle amount of a DNA sample.  Automated equipment quickly amplifies necessary fragments of DNA many times. Special machines determine the nucleotide sequence of those fragments. Scientists can further compare the samples obtained from a crime scene or legal inquiry and determine whom they belong.

    New development in DNA fingerprinting came with the discovery of STRs (Short Tandem Repeats). They are DNA sequences of only two to four nucleotide pairs in length similar to minisatellite DNA form highly individual pattern.  STR analysis is the most commonly used method for forensic identification.

    What are the limitations of the method?

    The most serious factor that can affect the results of fingerprint analysis is a quality of the sample. Any smallest contamination (including traces of DNA on the testing equipment and mixed body fluids from different people) can jeopardise the testing. Recent blood transfusions can also cause inaccurate results.