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Biology 103
2005 First Paper
On Serendip

Two of a Kind: A Study of Identical Twins and the Environment

Katie Driscoll

DNA testing has been used by law enforcement agencies around the world to convict the guilty and exonerate the innocent. Everyone's DNA is unique, making it the linchpin in solving many important criminal cases. At a crime scene, any remnants of hair, blood, semen or other bodily fluids are used by forensic scientists to profile and compare the DNA strands of the specimen to that of the suspect's (1). This seems like a flawless system: Simply match the DNA left at the scene of the crime with that of a suspect and there's your answer! Or is it?

Let's look at the case of Darrin Fernandez, who was arrested while breaking and entering a woman's house and tried to escape from the building while bleeding. The police took samples of his blood and found that the DNA from this sample matched the DNA obtained from two unsolved sexual assaults, each one taking place within a few blocks from where Darrin was arrested. Darrin was convicted of one of the two rapes, but could not be convicted of the second. In the second case, DNA was the only evidence recovered from the crime scene. In most cases, this would be more than enough evidence to convict a suspect. However, in this instance the DNA turned out to be a perfect match for two people: Darrin Fernandez and his identical twin, Damien (2).

Identical twins occur when a fertilized egg splits, creating two embryos with the same DNA, making it impossible to distinguish one twin from another using our current DNA analysis technology. Although identical twins only make up about 4/10 of 1% of the population and there are only between 3 and 10 serious criminal cases annually involving identical twins, it is still worth noting the apparent limitations of our DNA testing system (2).

However, recent research conducted by Mario F. Fraga, of the Spanish National Cancer Center, indicates that perhaps identical twins are not truly identical. Fraga studied 80 Caucasian identical twins from Spain ranging from ages 3-74, with a mean age of 30.6 years old and a standard deviation of 14.2 years. He used epigenetics to determine if there were any noticeable differences in the genetic makeup of these identical twins (3). In epigenesis, methyl groups are "added to specific sites on DNA and acetyl groups are added to the histone proteins that form the chromosomal structure around DNA, either silencing (through methylation) or promoting (through acetylation) the expression of specific genes" (4). In short, epigenesis relates to how genes are expressed by magnifying or reducing the effects of specific genes (5).

Fraga's results illustrate that in 65% of twins studied, there was no difference in epigenetic patterns on the DNA. However, 35% of twins exhibited epigenetic differences. Large epigenetic differences were associated with older twins who had different lifestyles, and had spent less of their lives together, illustrating the potential important role of environmental factors in creating epigenetic differences among identical twins (3).

Fraga's results have been useful for many fields of science, including psychiatry. Doctor Peter Roy-Byrne, Editor-in-Chief of "Journal Watch Psychiatry", recently published an article explaining the vital importance of Fraga's study in the field of psychiatry. He writes that Fraga's results can serve as a possible explanation for the frequency and onset of disease among identical twins. He explains that in the psychiatric field, psychiatrists study how one's experiences relate to one's genetic make-up to produce certain psychiatric illnesses. Doctor Byrne adds that Fraga's results can be of great use in explaining why some twins and siblings do not have the same illnesses and why some twins get the same disease but at different ages (4).

Fraga's study is important for understanding potential differences among identical twins and the idea that identical twins can actually have different expression of genes in their DNA is truly groundbreaking. However, I think that his research seems to raise the more important issue: How does the environment produce possible life-altering changes in DNA expression? Epigenetics can be an important tool to helping us understand the potential hazardous effects of the environment on all human being's health. It could be used to explain why a disease strikes one person and not another, even though neither one's DNA carries a disease-causing residue (6).

The notion that the environment can be a significant factor affecting one's livelihood, leads to me to question: Did we do bring this upon ourselves? The world we live in is not the same environment that our parents or grandparents lived in. Our world is constantly changing, especially as a result of developing technology and science. We have created this world, this environment that we are now finding may actually cause harm to us. For example, there are people who live near power plants, a man-made construction, who may be more prone to developing cancers and tumors as a result of living in this environment. While power plants do provide us with the energy needed to fuel our civil society, what are its effects on the people living near these plants? Is it worth exposing ourselves to these potentially hazardous environments for the sake of technology and the 'advancement' of our society? By advancing technologically, are we really progressing, or have we inevitably doomed ourselves to suffer the consequences of such 'progress'?

I realize that tests have been conducted in the past demonstrating that living in a particular environment and partaking in a certain lifestyle will inherently affect one's overall health. However, Fraga's observations really made me take a step back and put my own life in perspective in terms of my daily choices. I feel like we have tampered so much with our environment, from genetically engineering crops to building large nuclear power plants, to the point that we may actually be putting ourselves in more danger for the sake of science and capitalism. The idea that I am part of this general population that is affected by the environment makes me feel like a guinea pig in this technologically developed society that we live in.

Although Fraga's observations do not establish any Truths about science, his work will serve as a building block for progress and for further scientific exploration. His work does point out interesting differences between identical twins that could assist a wide-ranging spectrum of people in better understanding their field. Forensic scientists could work to create a new test that could use epigenetic differences to distinguish identical twins suspected in a criminal case. Doctors may be able to better understand why one twin may develop a disease much later than the other. On a much larger scale, it addresses the issue that our environment and personal lifestyle choices could play a major role in affecting our health. Furthermore, it leads one to question that in trying to 'evolve' and 'progress', have we only set ourselves up for self-destruction.


1) "DNA" on Wikipedia encyclopedia website

7) "Evil Twins." Legal Affairs Magazine. September/October 2005, pages 5-7.

3) "Epigenetic Differences Arise During the Lifetime of Monozygotic Twins" on the Proceedings of the National Academy of Sciences of the United States of America Website

4) "Emerging Perspectives: Epigenesis How Experience Sculpts Genes" on the Journal Watch Psychiatry Website

5) "Identical Twins Exhibit Differences in Gene Expression" article on Scientific American website

6) "Twin Data Highlight Genetic Changes" Washington Post Article

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