Tag Archives: meoosis

This immortal coil

DNA, they say, is the molecule of life. Its long threads can be found in almost every cell of your body. Every minute of every day, the many genes it contains are put through production lines to produce the bounty of proteins that are built into each cell type, from eye lenses to heart muscles.

But where did that DNA come from? Let’s take a trip back in time. Before every cell divides, it replicates every one of its 46 molecules of DNA, or chromosomes. When egg met sperm at the moment you came into being, two sets of chromosome came together, one from Mum, one from Dad. As your parents reproductive cells developed, your grandmother’s and grandfather’s chromosomes came together and for the only time during your parents’ lifespans, they swapped genetic information. The chromosomes then divided twice, again for the only time, to produce sex cells with only 23 chromosomes. The earlier shuffling meant that each chromosome wasn’t just Grandfather’s or Grandmother’s; it was a bit of both. This genetic shuffling has increased genetic diversity and has provided grist for the mill of natural selection.

Gaining reverse speed, going further back in time, this division and shuffling has happened as humans have evolved from less complex organisms such as fish-like creatures, multicellular organisms and single cell organisms. Where it all began is still a mystery, but the message is that molecules of DNA have been passed down all this way to you. Sure, they have been shuffled a lot on the way but they are effectively immortal. How will they continue to evolve? Who will they inhabit? Time will tell.

Richard Dawkins wrote a book on evolution he called “The Selfish Gene”. Although he regrets the title because some have interpreted it as giving genes a sense of purpose, he meant that the gene was at the centre of evolution and not the organism or social group. Dawkins suggested that in the beginning, a DNA molecule he calls the “replicator”, managed to reproduce itself and thus gain in number. He proposed that somewhere along the line, it gained the protection of a cell around it; a survival capsule. As the cell’s environment changed, DNA molecules needed to adapt to these changes or the organism would die and it would lose its protection. So it kept mutating until one version of itself helped the cell adapt to its new home and start dividing again.

Sometimes in their rapid charges to survive, genes survive but organisms don’t. Think about the species of spiders in which the male is eaten by his mate just after mating and passing on his genes. It has been argued that only recently tables have turned. We can now choose birth control and end its billion year life in your body when you die.

So maybe those of us who choose not to have children should give quiet thanks to our DNA and those that mourn for us when we go, should mourn for our DNA too, for it will have lost its immortality.

DNA

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