Gel Electrophoresis L/O - Describe how gel electrophoresis can be used to separate DNA fragments of different length. 2 3 How do we generate these genetic profiles? DNA molecules are negatively charged, so if you apply an electrical current to a medium they are present in, they will move towards it (the positive electrode). A DNA profile is created by comparing STRs (Short Tandem Repeats) or other genes of interest. Gel Electrophoresis Example: On the two chromosome 13s in your body the short tandem repeat characteristic of region D13S317 is ATCGATCGATCG. Then the number of ATCGATCGATCG repeats there can be used to compare you against someone else. Names of just a few STRs on our different chromosomes. Gel Electrophoresis uses an electric current to separate DNA based on size. The gel acts as a sieve for the DNA fragments. The smaller the fragment the further through the sieve the DNA travels. The gel is immersed in a buffer solution which conducts the electrical charge. If all goes well, you will end up with something similar to the left. In school experiments you can just apply a dye, but this is difficult to see. So there are other ways to visualise the fragments: -Attach fluorescent probes and use UV light -Attach radioactive probes and use photo film. These are types of gene probe that attach to targeted sequences of DNA. Alternatively, it may be preferable to transfer the profile to a more durable material such as nylon or nitrocellulose sheets. The samples will be drawn by the flow of water diffusing into a drier material into the nylon sheet. If al goes well you will have a Gene Profile. -Position of the bands -Thickness of the bands (may vary in some cases) -Number of bands shared/missing