When doing research it is important and helpful to reference papers about subjects that are the same or similar to what you hope to achieve. This week I’ve read several very helpful articles for extracting genetic information from hair samples. This will come in handy for gaining useful information from the samples that we collect this summer. Some of the things we can find out from genetics are: the species, sex, and age of the animal as well as family relationships. However, to find out so much information from samples requires a lot of complex study. We will be using genetic information to differentiate between species in our study.
One of the problems with gathering genetic information from the field is that DNA and other nucleic acids can be broken down quickly due to naturally occurring DNAse and RNAse. Hair is a good source of genetic information because, using certain techniques, you can get information from inside the (protected) hair shaft.
If you take a hair and cut it in half you would be able to see three layers under a microscope. The outermost is called the cuticle. The cuticle is made out of keratin which is a very tough protein. It’s the same stuff that your fingernails are made of. The next layer is called the cortex–this layer has the pigmentation that gives your hair its color. The final layer and the innermost part of the hair is called the medulla. One interesting fact is that humans are the only mammals that sometimes do not have medullae. Most animals have fairly large medulla that take up a large part of the hair. The medulla has cells in it that we can use to extract some genetic information. For more information on hairs and the source of most of this information, visit Anatomy of a Hair at: http://shs2.westport.k12.ct.us/forensics/09-trace_evidence/splitting_hairs.htm
Two papers that I read this week talked about using very small samples of hair to gain useful genetic data.
The first paper I read was called: DNA extraction from hair shafts of wild Brazilian felids and canids (Alberts et al., 2010). In this paper the scientists used only 2 to 3 hairs (or about 10 cm total hair length) to get enough DNA (one type of genetic data) to get useful information about the animals that the hair came from. This was interesting because they used a modified method from a paper from 1996 that was originally used to get DNA from feathers. The method was useful because it could break down the hard keratin layer around the hair’s medulla and allowed the scientists to get to the DNA in the center of the hair shaft.
The downside is this method takes a while to complete, about 105 hours or, for less mathematical wizards, a little over four and a third days.
Although it sounds fancy, this just means that the detergent has some enzymes (chemical products of some organisms that break down different substances). This means that the detergent has the added ability to break down proteins, fats, and starches, all of which helps get stains out. I’ve never really noticed enzymatic detergents advertised but they are common in many familiar brands including Tide, All, Gain, and Arm & Hammer detergents, to name a few. These enzymes are also useful in breaking down hair and allowing scientists to get to the genetic information.
The coolest thing about this paper is that they were able to extract DNA at a very fast rate. In fact, with this method Guan et al. were able to extract DNA in less than 2 hours! THAT’S INSANE, considering traditional methods take a few days. In their study they were able to demonstrate that they could amplify the small amount of DNA that they extracted from similarly small samples of hairs. In fact they actually got better results from smaller samples than from larger samples (although this result needs further investigation).
Using this information, we plan on trying out both of the above methods ourselves. We’ll be using domesticated dog, guinea pig, and human hair while running some of these trials in the lab.
Until next time,