Efficient production of food – whether it’s crops or animals – relies on two main features: producers try to select the genetic specimens that are best suited to particular environmental conditions.
It’s really just another version of the old “Nature plus Nurture’ paradigm, where Nature is represented by the DNA sequences in the genes, and Nurture by environmental stimuli of many types from irrigation levels to the amount of sunlight, and from seaweed in cattle feed to calcium levels in silage.
But have you ever wondered how genes and the environment communicate with each other? Why does winter barley need a period of cold before the genes that control flowering deign to wake up and start the process that leads to beautiful healthy grains?
It’s only really in the last few decades that scientists have begun to develop an understanding of what’s happening at a cellular level when organisms respond to their environment. It’s a field that’s incredibly complex and developing fast, and it has the potential to increase the efficiency of modern farming practices, increasing yield while minimising inputs.
This field is called epigenetics. ‘Epi’ comes from Greek and means ‘as well as’, in addition to’ or ‘on top of. It refers to a whole level of information that’s quite literally deposited on top of DNA molecules, changing the way that genes are expressed.
The easiest way to visualise this is if we think of DNA not as a blueprint or a template, but as a script. If you’ve ever seen two productions of the same play, you’ll know that they can look and sound completely different even though the two versions use the same words. During read throughs and rehearsals, the director and cast will have annotated their scripts with pencil marks, Post-It notes, highlighter pens etc and used these notations as prompts for how to deliver their lines. It turns out that something similar is happening all the time to DNA in cells, in response to environmental signals. A huge range of tiny specific chemicals get added to DNA and the proteins that are associated with it. They never change the sequence of the genes (the original DNA ‘script’) but they instruct the cell to use those genes in different ways. This can include turning them on or off or pushing gene expression up or down (analogous to an actor shouting or whispering his/her lines).
A dynamic system
The great thing about epigenetics is that it’s a very dynamic system. DNA itself can’t change rapidly in response to the environment during the lifetime of an individual, be it a broad bean or a boar. But responding quickly is exactly what the epigenetic system has evolved to do so it gives organisms a fighting chance when their environment changes, whether that’s a sudden decrease in rainfall or an equally sudden increase in salinity.
Because the system is dynamic, it also contains a degree of random flux. That may seem like a bad thing, but in terms of responding quickly to dynamic changes it’s actually incredibly useful. It means that in any population, whether of cells or individuals, there will always be some who are epigenetically better positioned than others to quickly make the additions to DNA that will allow that individual to roll with the environmental punches. It’s an inevitable consequence of an intrinsically noisy system.
Scientists actually recognised this randomness in biological systems about a hundred years ago. They realised that genetically identical mice, raised under identical laboratory conditions, varied in key aspects such as body weight. The researchers gave this phenomenon the name intangible variation’ which sounded great but didn’t mean anything. But now we know that this intangible variation is actually a manifestation of the noise in the epigenetic system.