One Gene, One Behaviour?

Erwin Schrodinger, the brilliant Austrian physicist, is best known for his wave equation that describes the movement of particles on a quantum level. Perhaps among his lesser-known contributions is that he laid the foundations of quantum or molecular biology in his book 'What is life?'.

Schrodinger was one of the first to hypothesise regarding the nature of the hereditary material responsible for the way we are. He suggested that if such a molecule exists, it would most certainly be an aperiodic crystal. This implied the presence of a molecule that was able to hold information using an aperiodic sequence of molecules connected by covalent bonds (related to the information theory interpretation of entropy, a blog post for another day). Schrodinger (as did most scientists) assumed that the most likely candidate were proteins, being composed of 20 different monomers called amino acids.

This was proven wrong in a few decades, with the establishment of DNA as the puppeteer that held the strings to life. Francis and Crick were hailed as the pioneers of a new age for biology (Apologies, Rosalind Franklin). Methods were developed to find out how stuff works, which lead to what we call the central dogma. Simply put: DNA makes RNA makes Protein. All we are was reduced to a tightly regulated clockwork of molecules that we now call life.

Now, I assume that the reader has some knowledge of how DNA works, so I'm going to skip right to the good bit. Genes produce proteins through a dizzyingly complex process, and proteins keep us alive by keeping those (and many other) processes running. This was neatly summarised in Beadle and Tatum's one gene-one enzyme hypothesis, which said that each gene produces one enzyme that affects one step in a metabolic pathway. 

But that's a bit too simple, yes?

What I think about is, whether genes affect our behaviour? Yes, yes. Anyone would agree that they do.

But, could we extend the one gene-one enzyme hypothesis to a one gene-one behaviour hypothesis? I mean, could one gene somehow contribute to a complex action or behaviour, as we might call it? There's data to support this, but we have yet to uncover the subtle intricacies of the issue.

I recall an experiment that Professor Dawkins mentions in his book The Selfish Gene. W. C. Rothenbuhler, an entomologist interested in the behaviour of bees, found that a complex behaviour for maintaining beehive hygiene was controlled by genetics. Grubs are sometimes affected by a disease called foul brood. Some strains, called the hygienic strains, get rid of this problem by committing infanticide (GASP!). That includes: locating the infected grub, removing the wax cap from its cell and dragging the poor thing out and yanking it off the hive.

Now, one might conclude that this behaviour is genetically determined. True. However, what's astonishing is that this complex behaviour can be sub-divided into its elements, as can be seen above. Cross-breeding between hygienic and unhygienic strains produced hygienic as well as unhygienic strains. However, a third strain went half-way. While it plucked off the wax cap on the grub's cell, it did not get rid of the diseased grubs. Further cross-breeding proved that the behaviours for uncapping and throwing out were defined by two genes. How fascinating.

Could it be that our behaviours are defined by our genes? Truly, they are. But, could we ever be able to know how? Surely, it is far more complex to understand how a gene might affect synaptogenesis (creation of connections between neighbouring neurons in the brain) in a brain as complex as ours, producing a defined behaviour. And despite its many triumphs, neuroscience is surely in its infancy, for we know more about what's on our mind than within it.

Could we identify genes that define our behaviours? And if we do, could we in the future, engineer humans that have certain behaviours built into them? Surely, we talk about designer babies (back in the news again. Thanks, CRISPR!), but the arguments are mostly limited to physical attributes and eugenics (humans are so obsessed with aesthetics, aren't they?). A good way to search for such genotypes would be to dice human behaviours into their fundamentals, and then, look for a genotype corresponding to each of those behaviours.

Some questions that arise are: Suppose we find a genotype that predisposes a human being to be more aggressive or violent. Wouldn't that correlation lead, inevitably, to genetic screens that would seek to identify such behaviours based solely on their genes? Would that be ethical? How much control do we have over our genetic impulses? How guilty are we for our follies, if we are cursed to follow our genetic destiny?