Simple humans

The acronym DNA and the word ‘gene’ are in common usage today but it was only in the 1940s that DNA was determined to be the genetic material, and DNA’s structure was not worked out till 1953. Then the race was on to find out how genes worked; a gene by definition being a stretch of DNA that codes for a particular substance. I had the great privilege to work on a small aspect of this in the early sixties for my PhD. In those days much of this work was done using bacteria for the simple reason that they have just one chromosome – a single thread of DNA. The bacterium that I worked with was a human pathogen called Pseudomonas aeruginosa. It gained a bit of notoriety around that time because it infected and killed the first heart-transplant patient; so I had to be careful. But my professor had chosen this species of bacterium because it had enzymes, and therefore genes, for digesting sugar in three different ways. We humans have just one way – the Embden-Meyerhof pathway. Pseudomonas had that plus two others. 

This was way before whole genomes came into the picture. It was assumed at that time that a bacterium would have about a thousand genes on its one chromosome. We hoped bacterial genomes would be fully elucidated one day, but doubted the human genome would be understood in my lifetime, and it was thought that it would probably entail mapping hundreds of thousands of genes. 

However, towards the close of the 20^thC estimates for humans were reduced to about 100,000 genes, a somewhat humbling figure seeing that E. coli had come out higher than originally expected with 4,485 genes on its single chromosome. Finally, with much fanfare involving President Clinton and Prime Minister Tony Blair a ‘rough draft’ of the human genome was announced in April 2000. What was not so widely publicized was that it was found that our genome only operated on about 30,000 genes. In 2012 I volunteered and had my entire genome sequenced, but even mine didn’t have any more. In fact in the few years since then, figures have been revised downwards so that latest estimates are closer to 20,000 genes, arranged on 46 chromosomes. 

But surely human beings are far more complicated and therefore require more genes on more chromosomes than other simpler creatures. Afraid not. Our ape cousins, chimps and gorillas, have 48 chromosomes, cows have 60, bears 74, and turkeys 80!  The gene count is even more humiliating: water fleas have 31,00 genes – fifty per cent more than we do; and even the simple Nematode worm, less advanced than the common earthworm, beats us with 21,000 genes. It’s even more humiliating when it comes to plants. Lowly mosses have around 32,000 genes, the cute little wayside flower Birdsfoot Trefoil has 40,000 and Poplar trees 45,000. 

There must be something wrong: how can this brilliant creature that’s put men on the moon, blown up islands with H bombs, polluted the planet to the extent that we’re buggering up the climate, and cut people’s heads off for not bowing to the correct god - how come we have so few genes?  Yeah, well.  

 

I'll leave you with a picture of cute little Birdsfoot Trefoil. But It takes twice as many genes to make this cutie which while pleasing us with its beauty above ground, does the amazing feat of fixing atmospheric nitrogen in its roots, thus enriching the soil for others.