Sunday 8 August 2004

Pic of the day: In the upcoming computer game The Sims 2 the Sims are supposed to have genes. Let's hope they have more than that.

Recipe for human soup

In the futuristic strategy game Alpha Centauri, one of the characters famously says that our DNA does not specify the position of each capillary in the body or each neuron in the brain. This is in itself worth noticing whenever we think of cloning or "identical" twins.

If cloning is completely successful, it results in a time-delayed twin. As anyone who knows identical twins will testify, they are rarely identical. At best they are physically identical, but their personality tends to be different, and more different when they grow up together than when they grow up apart. But even genetically identical twins have different fingerprints, and in extreme cases they may even be mirrors of each other - one lefthanded and one righthanded, for instance.

In practice, cloning is not so exact. It usually entails using an ovum from someone else, and that means at the very least that the new person gets the mitochondria of the ova donator. Mitochondria are the energy factories of the cell, and they have a powerful impact on your metabolism. They come with their own DNA and are not at all created by the DNA in the nucleus. (In normal human reproduction, mitochondria come from the mother. The sperm cells has a bunch of tightly packaged mitochondria that powers it on its long journey, but they don't propagate in the fertilized cell. If there are exceptions to this, they are few and far between.)

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It gets worse from here. The DNA itself is nothing at all like a blueprint. It contains only one kind of information, base triplets (sometimes called codons, especially when referring to RNA) that represent one out of 20 amino acids, or a stop codon that signals the end of a chain of them. By using this coded information to assemble amino acids, it is possible to create specific proteins, which are made from long chains of amino acids. However, we don't consist solely of proteins. We could not live even for a second without lots of other chemicals: Fats and sugars are important part of our cells, and of course water. But there is no mention in our genes of the correct amount of water, or sugar or starches or various lipids.

In fact, there is no mention of how to combine the many proteins into the structures in the cell, or even any hint on when to start producing a protein and how much is enough. These are things that the cells seem to know, all they need to consult the database for is the actual sequence of amino acids that go into the proteins.

Nor are the genes neatly laid ut in the order in which they will be most used, with functionally related proteinse side by side. No, they are scattered like tools in a junkyard. Indeed, much of our precious chromosomes consists of "junk DNA" such as remnants of old retroviruses, copies and defunct older versions of existing genes, and long strings of short repeating patterns that don't code for any protein known to man or beast. To complete the confusion, there are pieces of junk DNA inside our genes, so there is a stretch of useful DNA followed by pieces of junk that must not be decoded, then the gene resumes for a while only to be interrupted by more trash, and so on. Somehow the cells manage to start and stop at the right places, at least often enough that proteins are manufactured quickly and smoothly at need.

The human genome resembles nothing so much as a hard disk that has been used for many years and never been cleaned up or maintained in any way, and which now also lacks a file allocation table to show where the real data is inbetween the junk. Or for the less computer oriented, think of it as a recipe that is written in the margins and between the lines of a book that, on closer inspection, turns out to be an ape's attempt to recreate the complete works of Shakespeare. The recipe furthermore only lists some of the ingredients and no hints on how to prepare the dish, much less what it is supposed to look like when finished.

On this basis is all life made, and every human with our hopes and dreams.

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(For those of you who thought I would write about cannibalism ... eww! You can go read Stranger in a Strange Land though. There you'll find something more relevant for you, and it should also give a fresh perspective on the concept of "the Last Supper".)