One of the courses I’m taking this year is Genomics, the study of the structure, content, function, and evolution of DNA. Our instructor, Barrie Robison, began the course with an interesting statement on our first day:
“You all know the central dogma of DNA correct? Everything moves from gene to protein, with RNA in between?”
We all nod in agreement.
“Well, this class is all about messing with that concept. Seriously.”
There’s a lot more to DNA than just genes, and there’s a lot more to genes than just a data spew or “blue-print” for the cell to follow. Conveniently, the book I’m reading: Monkeyluv, by Dr. Robert Sapolsky is hammering on the topic as my Genomics course. I think Dr. Saposlky and Dr. Robison would agree that there are some heavy misconceptions among the American public about DNA.
Dr. Sapolsky notes that there are two major false assumptions: the notion that biological information flows outward from the genes (“nobody tells a gene what to do”), and that genes have overbearing influence (“when the gene commands, the cell listens”). This would be to say that genes have full power over all cell functions; they are the commanders of commanders!
These two assumptions are ingrained at a young age. I recall the middle school jokes about bad genes; anything that was possibly wrong with you, you could just shrug off and blame on your genes. Whether you were depressed, chubby, or not so great at math we were all singing the same tune that I still often hear today: “it’s just my genes.”
And yet, many of us know these assumptions must be false if we take a few minutes for deductive reasoning. If genes dictate every action of the cell, then why can our environment have so much influence on our biological functions? A cell cannot know from code alone that the weather’s getting hot or cold and it’s time to acclimate, that something good has just happened and it’s time to make you happy, or that it’s morning now and time to wake up. If genes were the end all dictators, then why do we even bother with upbringing? Why would we say good parenting is key?
A good example to stress that the same genes can have different results comes from my childhood experiences with the identical Cooper twins. I remember when we were all about six Ashley and Andrea Cooper looked a lot alike although they had slightly different personalities even then. By the time high school was over, the two had shaped into completely different individuals. Andrea was smaller with a different face due to “picky eating” growing up and an insatiable love for ballet. She was shy and a bit mousey. Ashley was slightly larger (although still quite slender) with an outgoing personality that had her pursuing and enjoying a life in the spotlight as a member of the drama club.
This could not be if genes where the determinant factors! Rather, a better analogy for the cell and genes would be to say that the cellular environment is like a great, busy community. The DNA is in the central office (the nucleus) but having a constant dialogue with RNA and proteins in the cytoplasm. Recall my article from a couple weeks ago on bipolar disorder and clock genes? Circadian rhythm was maintained by a constant interaction of DNA, RNA, and proteins. Proteins can feed back into the nucleus and have either inhibitory or excitatory effects. Proteins don’t have to be made within the cell by that DNA either. Chain reactions set off by proteins in the cell membrane can effect DNA, as can some hormones, like estrogen, that move directly through cellular and nuclear membranes to act on DNA. No gene has a mind of its own; you can’t simply put a pile of DNA somewhere and expect it to grow. This is why cloning often takes hundreds of tries—the correct cytoplasmic components in the egg of the parent must be present and active before life can begin.
I don't want to discredit DNA and genes too much, there are some genes that encode very specific traits (and diseases) and genes have a great influence on all of us, but there are many ways to control gene expression. It can be done indirectly by affecting the machinery of protein production (tRNAs, ribosomes, transcription factors…), by modifying the secondary code, RNA (alternative splicing, RNA modification, RNA interference…), or directly by physically moving or binding to the DNA. The DNA is never actually modified (unless unintentionally by mutagens), but it can be moved in such a way so that a less “useful” portion is buried deeper, it can be turned "on" and "off" by proteins, and it can be enhanced or insulated.
All of these factors come together to make an organism that is far more than just the sum of all its genes. We are products of every action, and interaction, of both our genes and environment.
Sources: Robert Sapolsky (left). Monkeyluv. 2005