Complexity_ A Guided Tour - Melanie Mitchell [131]
The questions of how, why, and even if evolution creates complexity, and how complexity in biology might be characterized and measured, are still very much open. One of the most important contributions of complex systems research over the last few decades has been to demonstrate new ways to approach these age-old questions. In this chapter I describe some of the recent discoveries in genetics and the dynamics of genetic regulation that are giving us surprising new insights into the evolution of complex systems.
Genetics, Complexified
Often in science new technologies can open a floodgate of discoveries that change scientists’ views of a previously established field of study. We saw an example of this back in chapter 2—it was the invention of the electronic computer, and its capacity for modeling complex systems such as weather, that allowed for the demonstration of the existence of chaos. More recently, extremely powerful land and space-based telescopes have led to a flurry of discoveries in astronomy concerning so-called dark matter and dark energy, which seem to call into question much of what was previously accepted in cosmology.
No new set of technologies has had a more profound impact on an established field than the so-called molecular revolution in genetics over the last four decades. Technologies for rapidly copying, sequencing, synthesizing, and engineering DNA, for imaging molecular-level structures that had never been seen before, and for viewing expression patterns of thousands of different genes simultaneously; these are only a few examples of the feats of biotechnology in the late twentieth and early twenty-first centuries. And it seems that with each new technology allowing biologists to peer closer into the cell, more unexpected complexities appear.
At the time Watson and Crick discovered its structure, DNA was basically thought of as a string of genes, each of which coded for a particular protein that carried out some function in the cell. This string of genes was viewed essentially as the “computer program” of the cell, whose commands were translated and enacted by RNA, ribosomes, and the like, in order to synthesize the proteins that the genes stood for. Small random changes to the genome occurred when copying errors were made during the DNA duplication process; the long-term accumulation of those small random changes that happened to be favorable were the ultimate cause of adaptive change in biology and the origin of new species.
This conventional view has undergone monumental changes in the last 40 years. The term molecular revolution refers not only to the revolutionary new techniques in genetics, but also to the revolutionary new view of DNA, genes, and the nature of evolution that these techniques have provided.
What Is a Gene?
One casualty of the molecular revolution is the straightforward concept of gene. The mechanics of DNA that I sketched in chapter 6 still holds true—chromosomes contain stretches of DNA that are transcribed and translated to create proteins—but it turns out to be only part of the story. The following are a few examples that give the flavor of the many phenomena that have been and are being discovered; these phenomena are confounding the straightforward view of how genes and inheritance work.
Genes are not like “beads on a string.” When I took high-school biology, genes and chromosomes were explained using the beads-on-a-string metaphor (and I think we even got to put together a model using pop-together plastic beads). However, it turns out that genes are not so discretely separated from one another. There are genes that overlap with other genes—i.e., they each code for a different protein, but they share DNA nucleotides. There are genes that are wholly contained inside other genes.
Genes move around on their chromosome and between chromosomes. You may have heard of “jumping genes.” Indeed, genes can move around, rearranging