I learned about restriction fragment length polymorphisms (RFLP) in my life science class last quarter. It amazed me that a one-nucleotide change in DNA can help distinguish people with certain characteristics. A RFLP is a single base pair change in the DNA sequence that varies greatly among individuals. This change overlaps with regions of the DNA that code for a restriction site, or a specific palindromic sequence where a specific enzyme cuts the DNA, thus changes in this site determine if that fragment of DNA is cut. Some of these RFLPs are linked to disease alleles, meaning that they are located very closely to a region of DNA that codes for a disease. These sites, therefore, can be used to detect a diseased allele in genetic testing. If a specific RFLP is located near a diseased allele, then the fragment pattern created by that RFLP will differ between different individuals based on if they have the RFLP linked to the disease. This analysis is done to compare family members, usually to determine if a child is at risk for a disease. If the parents are both heterozygous for a disease (have one normal and one diseased gene), RFLP analysis can be used to link a fragmentation pattern to that disease and if the child’s DNA has that fragment pattern, then they have the disease.
An example of how RFLP works. http://www.ncbi.nlm.nih.gov/genome/probe/doc/TechRFLP.shtml
This type of analysis has been dubbed “DNA fingerprinting.” This is because the pattern created by analyzing the DNA of different people are usually different if the trait being examined is different and can thus be used to identify a person. This term is slightly flawed and causes many misinterpretations about what the technique actually does. This is the point of the essay written by Paul Vanouse. He is an artist who has done a few pieces dealing with the way in which the general public perceives DNA analysis techniques. He discusses the fact that the DNA image generated depends not on the person, but on the technique used to create the banding pattern. He discusses the use of VNTR (variable nucleotide repeat regions) that, like RFLP sties, differ between individuals. VNTRs are regions in which a small short DNA sequence is repeated, but the number of repeats is variable. The fingerprint created using this technique and a fingerprint created using RFLPs could both be able to differentiate two people, or it is possible that only one would be able to differentiate them, especially if the individuals are related. Vanouse puts it this way: “These processes are cultural: images have been constructed based on the state of our understanding of DNA, and the instantiation of method has been a complex social process.” A fingerprint created for an individual will vary based on who is doing the analysis. This is not a fingerprint because this term invokes the idea that it is unchangeable and is dependent on the person from whom it came and not from the person who analyzed the sample.
Vanouse has incorporated this idea into his piece Latent Figure Protocol. He used varying enzymes to cut the same piece of DNA to form different fragmentation patterns, and when these patterns were run on a gel they created an image. The irony of this piece lies in the fact that the image created by the banding pattern is more descriptive of the animal from which the sample came than the banding pattern itself. For example, he created an image of the copyright symbol using the bacterial plasmid pET-11a as the template. He added varying restriction enzymes to create the different banding patterns seen. Each lane contains the same DNA, just fragmented in different ways. A bystander would not necessarily know that the DNA all came from the same source because each lane is different. The copyright symbol, however, is more descriptive of the DNA source. Different companies sell plasmids and they are promoted in the same way that all consumer products are. Plasmids have codes for varying restriction sites, protein tags, drug resistance, and other biologically relevant tools. For example, I use the plasmid pET-20b in my research because it contains ampicillin resistance and it has a histidine tag that is used to mark my protein of interest.
The term “DNA fingerprint” may not accurately describe the techniques that are used to create these banding patterns, but that does not mean that these banding patterns are not useful. They do not necessarily fingerprint a person, but rather they fingerprint a characteristic of that person. This means of identification is, in my opinion, most useful for disease screening, as I described in the first part of this post, and for research. I can use banding patterns to check to see if my gene that I inserted into my pET-20b vector was successful or doctors can use banding patterns to look for diseased alleles in a family. Overall these techniques are very useful to learn more about something that we cannot see, even if the word used to describe it is somewhat misleading.
An image of a DNA gel I took in the lab to check for a specific band in sample of interest.
And just for fun, a scientist used a technique similar to the one Vanouse used to create his artwork to propose to his girlfriend! http://www.theblaze.com/stories/2012/12/24/this-could-be-the-most-interesting-or-nerdy-marriage-proposal-you-will-ever-see/
Hartwell, Leland, Michael L. Goldberg, and Janice A. Fischer. Genetics: From Genes to Genomes. 5th ed. New York: McGraw-Hill Education, 2015. Print.
"PET11a." Addgene Vector Database (Plasmids, Expression Vectors, Etc). N.p., n.d. Web. 15 May 2016. https://www.addgene.org/vector-database/2625/
"Restriction Fragment Length Polymorphism (RFLP)." NCBI. N.p., n.d. Web. 15 May 2016. http://www.ncbi.nlm.nih.gov/genome/probe/doc/TechRFLP.shtml
Vanouse, Paul. "Discovering Nature, Apparently Analogy, DNA Imaging, and the Latent Figure Protocol." Tactical Biopolitics: Art, Activism, and Technoscience. Cambridge, MA: MIT, 2010. 177-92. Print.
Vanouse, Paul. "Latent Figure Protocol." Paulvanouse.com. N.p., n.d. Web. 15 May 2016. http://www.paulvanouse.com/lfp.html