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Restriction fragment length polymorphism (RFLP) is a technique used to qualitatively distinguish between different alleles of a gene. It works like this: Restriction enzymes are enzymes that cut DNA at specific symmetric sequences, for example: 5'-ATA|TAT-3' 3'-TAT|ATA-5' ("|" represents the restriction or cut site for one such enzyme) If you were to fluorescently label these DNA strands and run it on a gel, you would get one fluorescent band that represents the point to which the digested DNA migrated during the electrophoresis procedure. Another allele of the gene could have a slightly different sequence, for example: 5'-ATTTAT-3' 3'-TAAATA-5' You'll notice the sequence is no longer symmetrical, so our restriction enzyme from before will not recognize it and so will not cut it. If these strands were again fluorescently labeled and run on a gel, you would see a fluorescent band that did not travel as far as that of the first DNA sample. This occurs since the undigested DNA fragment is larger and so cannot migrate as far in the gel. Therefore, the banding pattern you would see could be different for different combinations of alleles. For an individual homozygous for the first allele, you would observe one band far along the gel. For an individual homozygous for the second allele, you would observe a band not as far along the gel. For a heterozygote, you would observe bands at both positions. Many different banding patterns can be generated by using different alleles and restriction enzymes. As for research, I guess one application would be for associating molecular markers or genes with different diseases or phenotypes. You could see if all individuals with a particular disease have the same banding pattern for a restriction site located within a gene suspected to cause the disease, and compare it to a control group. If you need me to clarify anything, please let me know :)