The Omega Expedition - Brian Stableford [124]
All of which would have been no more than mildly interesting, story-wise, had the plot not been thickened by two further elements.
Whereas the Earthly ecosphere only has one family of fundamental genetic molecules — comprising DNA and its close variant RNA — the Tyrian ecosphere had two. One was a “DNA-analog” which, in purely chemical terms, was a distant cousin to our own and to a number of other analogs animating primitive ecospheres on other worlds. The other was quite different, and so far unique.
I’m no biologist so I didn’t find it easy to follow the explanation Alice gave, but I think I got the gist of it.
The reproduction of Earthly organisms is a very complicated process, but it has two fundamental components: the reproduction of raw materials and the reproduction of anatomy. What genes do, for the most part, is provide blueprints for all the proteins that make up our bodies. Different kinds of cells use the blueprints in subtly different ways, producing slightly different sets of products, with those common to numerous cell types sometimes being produced in different quantities. The different cell types then have to be arranged into tissues and organs, and these too have to be distributed according to an anatomical scheme.
You might expect that the blueprint for bodily form would also have to be chemically coded into a set of genes, but it’s not as straightforward as that. There are bits of DNA whose function is to regulate the productivity of other bits of DNA, so that cells can be differentiated into a series of functional types, but the switching system is a simple one. In the same way, there are bits of DNA that are implicated in the way that different cell types are aggregated into tissues and organs, but their control system is also fairly simple. The process which determines whether an Earthly egg cell produces a cell mass that develops into a man, a bee, a crab, or an ostrich, consists of subtly different modifications of a surprisingly simple set of rules, whose application and enforcement have a lot to do with the environment in which the egg cell produces its embryo.
Figuring out how to simulate and direct an appropriate embryonic environment in an artificial womb was the breakthrough that made Conrad Helier a hero. The genes involved in the process are known as homeotic genes, and because they’re clustered together the whole outfit is sometimes called a “homeobox.” On Tyre, where the whole system works differently — because there is no process of embryonic development — the local equivalent of the homeobox isn’t just a few extra bits of DNA thrown in with all the rest; it’s a whole other ballgame. On Tyre, the biochemical system determining the form of organisms is quite separate and distinct from the DNA-analog system providing the raw materials out of which bodies are built.
The existence of the Tyrian example broadened the scope of comparative genomics considerably, and opened up the prospect of genomic engineering: the possibility that Earthly genomes might be remodelled at the most basic level so as to broaden the options open to artificial organisms. More profoundly, it opened up the possibility of genomic hybridization: of combining Tyrian-style homeoboxes with Earth-style chromosomes. The basis for some such technology was already present within the physiological processes organizing the chimerization of Tyrian organisms.
To put it crudely, once humans had arrived on Tyre there was a possibility — imaginatively farfetched but seemingly practicable — that Tyrian chimeras might be persuaded to take on DNA components, thus generating components of a hybrid ecosystem. The problems involved in persuading Tyrian soil to grow crops capable of nourishing human beings might be solved at a stroke. In the longer term, the possibility seemed to exist of arranging a