Reductionism

A recent article in the journal Science announced a stunning and exciting new finding:

individuals with one or two copies of the short allele of the serotonin transporter (5-HTT) promoter polymorphism, which has been associated with reduced 5-HTT expression and function and increased fear and anxiety-related behaviors, exhibit greater amygdala neuronal activity

OK, maybe it's not all that exciting at first glance!  Science is full of reductionist jargon, and scientists don't appreciate it when you try to draw abstract conclusions based on the narrow experimental evidence.  In any case, here's my interpretation of the article:

Everyone has the same 20,000 genes.  One of those genes is called SLC6A4 (previously called 5-HTT).  However, different people have different versions of that gene, the long variant and the short variant.  [If you really want to know the technical details, the long variant has 16 repeats of a 44 letter DNA sequence, and the short version has 14 deletions of that repeated sequence, called a "copy number variation" (CNV)]

Technically, the genetic difference lies in the so-called promoter region (or "on switch") just in front of the gene, not in the gene itself.  But in any case, it's all DNA.  Specialized proteins (called "transcription factors") latch onto this promoter region, looking very much like highway paving machines.  The promoter region (short or long variety) acts as the construction supervisor, telling the machine how much protein to make based on the gene template (or how much pavement to lay down).

It turns out that people with the short version of the gene have a more active amygdala, a structure in the brain (see the red area in the top picture) involved in processing negative emotions, and thus they have a greater response to fearful stimuli than people with the longer variant of the gene.  Your genes at work!

Correlation is not the same as causation, of course.  For example, people with the HLA-A1 gene variant tend to use chopsticks, but that doesn't mean HLA-A1 causes the use of chopsticks.  It's simply a more common gene variant in Asians than Caucasians, and Asians tend to use chopsticks.  If you wanted to prove that HLA-A1 was the "chopstick gene", you would have to show (among other things) the contrapositive, that Asians who don't use chopsticks also don't have the HLA-A1 gene variant.