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The gel-separated DNA fragments are then transferred to white nitrocellulose paper, so the paper now carries an exact replica of the DNA on the gel. The Southern blot equipment is quite Heath Robinson, involving trays, paper towels, and lots of solutions so can get quite messy.Heavy books are placed on top of the towels to squash everything down. Adding the radioactive probe This is the clever bit.
There would be a DNA sample from several people, each sample in a different hole.
The gel is made from something called agarose (derived from seaweed) and is just a pure firm jelly.
Most of the method I have described is quite routine in the lab since the late 1970s and not developed by Alec but by Ed Southern at Oxford (hence “Southern blotting”).
Alec’s particular contribution was the choice of the “probe”.
Identification of cultivars and selections, pedigree analysis, estimation of genetic relatedness and genome mapping — all of these objects are achieved with various methods of DNA fingerprinting which can distinguish even closely related genotypes.
Initial results were obtained by a variation of the well-known RFLP-technique (Restriction Fragment Length Polymorphism): hybridization of restriction enzyme-digested DNA samples with hypervariable minisatellite DNA probes.
Technical improvements, including a number of additional DNA probes and various DNA fragment detection methods, have since been published.
With the recent advent of the PCR technique (Polymerase Chain Reaction) and PCR-based methods like RAPD (Random Amplified Polymorphic DNA), DNA fingerprinting has widened its applicability and attracted a growing number of scientists.
Colour here is artificial – DNA is normally pink under ultraviolet light.
Transferring the DNA onto paper The gel-separated DNA fragments (the smear shown above) are converted to single stranded fragments by dunking the gel in weak acid, so that the DNA letters are exposed, rather than being in the middle of the double helix.