DNA Fingerprinting

by Georgina Cornwall, PhD

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    00:00 which brings us right into the topic of DNA fingerprinting where we will get the meaning of those RFLPs and STRs whatever those are.

    00:10 RFLPs are restriction fragment length polymorphisms. RFLP is much easier to say. Again STRs are short tandem repeats and both of them are going to be identified using gel electrophoresis and we will also use our old friend, restriction endonucleosis, restriction enzymes to cut up fragments of DNA. RFLP technology is an older technology that we have utilized for a number of years to do DNA fingerprinting, but more recently we have moved to short tandem repeat technology and that is the current norm in our crime scene investigations. Let us look at what this really means. Restriction fragment length polymorphisms. Polymorphism is the keyword here. Polymorphism means that we can acquire a different shape or a different size or a change in the genetic code. And DNA fingerprinting really is comparing the fingerprints, not the fingerprints but the fingerprint of the DNA or really comparing fragment lengths in DNA. Let us look at how we might acquire differences in fragment lengths. These regions that we find in RFLPs involve repeated sequences of DNA. We might have the same phrase, sort of repeated over and over and over. We could acquire variation in length, let's say if we had crossing over and it was slightly uneven during meiosis because the sequence reads the same, these accidents can happen pretty frequently. There is quite a bit of variation or polymorphism in these regions of RFLPs. Looking at our original sequence, for example, we will keep it very simple. We have one restriction endonuclease that is going to cut at specific RFLPs sites. You can order these. They are pretty well-identified regions around the RFLP and so we cut it at particular sites. In this case, we will end up with two fragments, a gene of interest particularly may be if we were looking at a particular gene and gene of interest on one fragment. And then when we run that through a gel, we will see a particular banding pattern. You will notice these two are fairly close to each other relative to what is going to happen next. Let us say we have a translocation event where a little piece of DNA extra RFLP ends up on the complimentary chromosome or non sister chromatids in that crossing over event. This restriction fragment length may increase and if that restriction fragment length increases, when we introduce the restriction endonuclease, we end up with two different pieces of lengths of DNA. One, at least, different length of DNA maybe two.

    03:20 And so when we run it to the gel, we will see a different banding pattern in the gel. Now we would have to use many different RFLPs in order to get a DNA fingerprint. As I had mentioned earlier, we now use STRs which are short tandem repeats. Before I show you what a fingerprint might look like because essentially it looks the same, let us introduce short tandem repeats.

    About the Lecture

    The lecture DNA Fingerprinting by Georgina Cornwall, PhD is from the course Biotechnology.

    Included Quiz Questions

    1. Variations in homologous DNA sequences
    2. Variations in homologous RNA sequences
    3. Similarities in heterologous DNA sequences
    4. Variations in homologous mRNA sequences
    5. Similarities in heterologous RNA sequences
    1. Gene cloning onto vector
    2. Genome mapping
    3. Localization of genes for genetic disorder
    4. Determination of disease risk
    5. Paternity testing

    Author of lecture DNA Fingerprinting

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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