Everything that you are comes from the four letters repeated millions upon millions of times in your DNA, right? Wrong. During this unit, we have begun to learn about Epigenetics, the markers and orientations in your DNA that can influence who you are almost as much as your DNA itself. Last week, we spent time watching the documentary Ghost in Your Genes. This documentary is all about the possibilities that epigenetics opens up, the research that scientists have already done, and what we already know.
When scientists originally mapped the human genome during the 1990’s, they were shocked to learn that there are only about 25,000 genes written in our DNA. This was surprising because scientists believed we were much more complex than other organisms, so our DNA must vary greatly. This is not true. In fact, humans share almost all of our DNA with various organisms, varying by only a few percent from chimpanzees, and even sharing almost 50% with a banana.
These similarities and the difference in expression have been linked to Epigenetics. In the cell, DNA is coiled around proteins known as histones. the tighter the DNA is wrapped around these molecules, the harder it is for the body to read it, and these genes are essentially turned off, or blocked from view. When this happens, the blocked genes will not be expressed. Similarly, genes that are more spread out will be read and expressed by the body. Another group of molecules, down as methyl tags, attach to the DNA as it is wrapped around histones, and help control whether a gene is turned on or off.
One of the studies that I found the most interesting in the documentary was done on Agouti mice. These mice have a gene known as the Agouti gene, which can drastically change the behavior and appearance of the mice. If the Agouti gene is turned off, the mice are a brownish grey in color, and are what you’d typically expect of mice, small, skinny, hyper, etc. If the Agouti gene is turned off, however, the mice tend to resemble Gus from the animated version of Cinderella. They are lighter in color, and eat nonstop. The side effects of this are obesity and disease, often related to the overeating. These yellow mice usually die much younger than their brown counterparts. This phenomenon was attributed to the epigenome after a study was done with mice who were identical twins, meaning they had the exact same DNA. One, however, had the Agouti gene turned on, while the other had the gene off. These mice displayed these two completely different personalities and two completely different appearances, even though they were genetically identical.
The idea that two genetically identical organisms can look so completely opposite each other, simply due to molecular tags is fascinating. The entire documentary was full of experiments like this. Identical twins are key to the study of the epigenome, because two genetically identical individuals that are not completely identical in the traits they show can only occur because of changes in these markers. Another thing that was interesting is that the epigenome can be changed over the course of ones life, by cigarettes or alcohol or simply too much sun. These changes, though somewhat easy to make, are hard to get rid of, and can be seen generations down a family line. Two scientists in Europe studied a town prone to famine, and found that there was a number of direct correlations between grandfathers food supply and their male descendants healthy and similarly for granddaughters and their grandmothers.
Epigenetics hold the key to so many questions scientists have had about human genetics for decades, and there is still so much more to learn. As this field moves forward, scientists are hopeful that keys to cancer, autism, and even Alzheimers might start to emerge. There is no telling how much we will be able to know and learn and heal using epigenetics, but we are living in such a time that we will likely be alive when many of these fascinating discoveries are made.
AP Biology 