Thursday, November 10, 2005

Epigenetics

Another one of Bryan Appleyard's targets last weekend was Horizon.

"This was once a co- production with public television in America, but, as a result of a BBC deal with the Discovery Channel, it has had to go more “mainstream”. Mainstream, in this context, means worse. Americans like action — such as pointless dramatisations — and they like to see what you are talking about, hence more pointless dramatisations. If you don’t lose the will to live and do make it to the end, you will have learnt precisely nothing."

Last week's programme set about telling us how prevailing theories of inheritance have been turned on their head by recent discoveries. There was indeed a fair deal of septic-stirring sensationalism, perhaps not all merited by the starting revelation - an interesting discovery made by Dr Marcus Pembrey of the Gt Ormond Street hospital that children with exactly the same deletion on one of their chromosomes showed the charateristic signs of two entirely different syndromes (Angelman and Prader-Villi)

Yet the key point here is indeed startling - our genetic inheritance is more than the sequenced chemical code of DNA; there's also a supplementary system of meta information that imprints our genes with information about their origins. This extra layer of complexity may explain why we have around 30,000 genes in total, not much more than a house plant. What matters isn't just the map, but which parts of it are tagged as on or off and why.

In the case of Pembrey's children the genome knows whether the deletion came from the mother or the father. The programme further suggested environmental or lifestyle factors that affect us during our own lifetimes can influence the imprinting of the genes of our children: in effect a watered-down version of the inheritance of acquired traits.

I wonder what Richard Dawkins makes of all this. Any kind of meta-genome would certainly shove a major spanner into Selfish Gene theory, at least in its purist form. Other Neo-Darwinists like Daniel Dennet might also sneer at the suggestion that the formulae of evolution operate on multiple, not necessarily complementary levels. Darwin on the other hand would probably have welcomed this partial reconciliation with the discredited Lamarckian model.

In this context The Human Genome Project now looks rather like Deep Thought's first outing - instead of revealing coming up with the answer to end all answers , it revealed a hitherto unanticipated, deeper problem.

The science of epigenetics clearly has a long way to go and this Horizon documentary ended up posing a lot of questions that it didn't even attempt to tackle. Here are a couple:


  • Is the system of imprinting an adaptation, or is as fundamental as DNA itself?
  • Whilst we may keep the same sequence of genes throughout our lives their activity varies greatly during the lifecycle with many changes occuring late on, long after we have had our best chance to pass them on. Does the meta-genome exist to support individual survival or is it also part of another system operating at group level?



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