Because of this, perhaps, genes have captured our collective imagination. They are to science fiction of the last twenty years what nuclear power was to science fiction of the forties and fifties: a deep, mysterious, vaguely ominous prospect, the gateway to both a brave new world of scientific achievement and a dystopian realm of apocalyptic nightmare.
And certainly, genetic science has done a lot for us. It has allowed us to assess our individual risk for a whole host of diseases, from cancer to heart disease to alcoholism. It has revolutionized the ways in which we fight many of these diseases. Heck, I even got paid to write a book about it. So if you ask me, genetic science is pretty swell.
But considering how fascinated we the public are with our genes, it seems strange that we don't know all that much about them. Or perhaps the bigger problem isn't that we don't know much about genes, but that most of what we think we do know is at least partially wrong.
This subject deserves more than one post, so expect subsequent entries into the Genes Unzipped series (as well as a TV show tie-in, movie franchise, and unappetizing brand of Gene-e-O's breakfast cereal). For now though, I'll focus on a single issue: that of the oft-touted phrase "gene for [insert headline-catching disease, skill, or behaviour here]."
The tricky thing about this "fact" is that it seriously oversimplifies a nuanced issue by implying that a gene "causes" something, meaning that a tiny sliver of an organism's genotype is single-handedly responsible for a complex problem in its phenotype*.
This is especially misleading when applied to behavioral traits like alcoholism, drug addiction, and ADHD, which, though certainly heritable and possessed of a genetic component, are determined in large part by the environment.
Consider the Dopamine Receptor D4 (or DRD4) gene. I have a lot to say about this notorious little gene, and it may very well become the subject of its own post. For now, suffice it to say that DRD4 comes in a number of different varieties called alleles. One of these alleles is called the 7-repeat (so named because it contains a nucleotide sequence that repeats 7 times), an infamous mutation that stands accused of countless crimes against humanity.
Studies have tied DRD4's 7-repeat allele to addiction, disorganized attachment, ADHD, aggression, and excessive risk-taking, among other conditions. Many if not most of these studies have proved a strong correlation between 7-repeat and every one of these behaviours.
The only problem is, 7-repeat didn't cause a single one of them. And the studies never claimed they did.
What 7-repeat does is increase a person's susceptibility to the environmental factors that promote these behaviours. Children with 7-repeat alleles are more likely to suffer from addiction or excessive aggression or ADHD, but only when they grow up in abusive, neglectful, impoverished or otherwise "at-risk" homes.
For example, if you have the 7-repeat allele of the DRD4 gene and you do heroin, you are statistically more likely to become addicted to it than someone with a different version of the gene. But 7-repeat doesn't perch on your shoulder like a cartoon devil, goading you into leaving your nice suburban home, hitchhiking to the rough end of New York City, and picking up some smack. If you're never exposed to drugs, and if you grow up in a supportive, nurturing environment where the emotional disturbances that lead to drug use never occur, no gene can force you to start using.
News articles trumpeting the discovery of a "gene for" this or that are often misleading, the result of poetic license or simply lazy journalism. There are diseases that truly stem from a single genetic mutation, and have essentially no environmental cause-- cystic fibrosis would be the most well-known of them-- but for the most part, diseases are caused by a combination of the two.
All this is not to say that genetic testing isn't important. It is, for all sorts of reasons, But it's important not to succumb to genetic determinism, where every disease and misfortune and challenge stems from the chromosomal soup swimming about your cells.
*phenotype refers to the sum total of an organism's observable characteristics. It stands in contrast to the genotype, which simply means the heritable characteristics coded into our genes. The phenotype encompasses the genotype plus any and all epigenetic and environmental influences that contribute to development. The genotype is the blueprint; the phenotype is the building. You need a blueprint to build a building, but you also need a foundation, building supplies, and workers to put it together.