THE PROUD AND STUBBORN GENES

A GENE IS NOT SO EASILY DEFINED

I found this material by Richard Dawkins quite interesting. It seems that when the father’s and mother’s chromosomes join to make the first cell, the bits and pieces of their chromosomes fit together quite haphazardly as pieces of one “cross-over” to bits of the other.

“A gene is defined as any portion of chromosomal material that potentially lasts for enough generations to serve as a unit of natural selection.” —Richard Dawkins

This is his photo on twitter

And furthermore: “Individuals are not stable things, they are fleeting. Chromosomes too are shuffled into oblivion, like hands of cards soon after they are dealt. But the cards themselves survive the shuffling. The cards are the genes. The genes are not destroyed by crossing over, they merely change partners and march on. Of course they march on. That is their business. They are the replicators and we are their survival machines. When we have served our purpose we are cast aside. But genes are denizens of geological time: genes are forever.

“Genes, like diamonds, are forever, but not quite in the same way as diamonds. It is an individual diamond crystal that lasts, as an unaltered pattern of atoms. DNA molecules don't have that kind of permanence. The life of any one physical DNA molecule is quite short—perhaps a matter of months, certainly not more than one lifetime. But a DNA molecule could theoretically live on in the form of copies of itself for a hundred million years. Moreover, just like the ancient replicators in the primeval soup, copies of a particular gene may he distributed all over the world. The difference is that the modern versions are all neatly packaged inside the bodies of survival machines.

“What I am doing is emphasizing the potential near-immortality of a gene, in the form of copies, as its defining property. To define a gene as a single cistron is good for some purposes, but for the purposes of evolutionary theory it needs to be enlarged. The extent of the enlargement is determined by the purpose of the definition. We want to find the practical unit of natural selection. To do this we begin by identifying the properties that a successful unit of natural selection must have. In the terms of the last chapter, these are longevity, fecundity, and copying fidelity. We then simply define a 'gene' as the largest entity which, at least potentially, has these properties. The gene is a long-lived replicator, existing in the form of any duplicate copies. It is not infinitely long-lived.” —Richard Dawkins in The Selfish Gene (1989 paperback edition), p. 35.