Thursday, May 29, 2008 - 11:52
RFLP is an acronym that stands for "Restriction Fragment Length Polymorphism." That's quite a mouthful and once you've said this phrase a few times, you realize why we use the initials instead. I know a Restriction Fragment Length Polymorphism sounds like something that must be impossibly complicated to understand, but if we take the name apart, it's really not so bad. Let's start with most familiar one of the four words and work from there. My guess is that for many of you, that word is "length." When we talk about length in this context, we are talking about the length of a piece of DNA. We measure DNA length in terms of smaller subunits that we call "bases" and when we talk about the size of a piece of DNA, we describe it by using the number of bases or even the number of thousands of bases (kilobases, or kb). Thisis like describing the length of a necklace by referring to the number of beads. The next term, that you might be able to guess at a bit is "fragment." A fragment is a piece of something bigger. With DNA, those fragments represent pieces of DNA that are smaller than the piece we started with.
We distinguish between RFLPs by using the length of different DNA fragments. The rate of movement for a piece of DNA through a gel or capillary depends on it's size. Big pieces move slower than small pieces. The next word is "Restriction." I'm going to stay away from this term now, but there's a cool story that goes with it. For now, we'll just combine this term with the word "fragment." A restriction fragment is a piece of DNA that's made by allowing an enzyme, a restriction enzyme actually, to cut the DNA. These enzymes are picky. They only cut DNA if they find the right sequence of bases - if we think back to our necklace, that would be like a certain sequence of beads. On to the last term and the end of the story. This word, "Polymorphism," means "multiple forms." A polymorphism in the case of our restriction fragment lengths, means that the fragments can have different sizes, usually two. Here's what this looks like when we use DNA fragments with fluroescent labels and view the image on a computer monitor. One last bit of information, since we are using this method to find out something about the genotype, we can also say that RFLP analyses are a form of genotyping or genetic testing. Related posts: Genetic Variation I: What are SNPs?