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Date:

September 27, 2001

Subject:

Mutation calculations

 

From: Tony Trewavas

Subject: Re:reference?



Dear Prakash,


I wonder if you can float out the following calculation for criticism.


I estimate that there are 10
15

individual plants of Arabidopsisi thaliana currently alive with on average three generations/year. With a mutation rate of 1 in a million that makes 10
9

mutant plants presently extant. Over evolutionary time that Arabidopsis has existed supposedly 25 million years is a reasonable estimate, that makes a total of 75x 10
15

mutants. Since there are about 25,000 genes in Arabidopsis that indicates on average each gene has received 3x10
12

mutations. Assuming that only the 150,000 bases are what figures in mutation, every base will have received full variation in combination with enormous numbers of others and with rearrangements, gene movement, insertions, transposition, frame shifts and everything else. The protein kinds and combinations which this represents are impossible to imagine they are so vast but surely cover anything we as scientists could envisage ever being able to express in plants by genetic manipulation. Constraints are exerted on what can be expressed and the organism survive. Those constraints are multiple existing separately at the molecular, cellular, tissue and whole organism level and in turn with the individual in the ecosystem with other individuals and species. And yet Arabidopsis for all this astronomical degree of experimentation is still just a weed, not a superweed. Furthermore each Arabidopsis plant produces on average say 5000 seeds of which only one will probably survive to become the new individual. I also believe that every individual can be distinguished genetically from every other individual in certain traits. Thus in combination the number of genetically-distinct Arabidopsis individuals that have emerged over the last 25 million years is 3.75x10
26

.


The greens would have us believe that scientists putting a few dozens of genes into crop plants every year are going to manage something nature has not contrived in experimentation 10
25

larger. To put this figure in perspective the universe has existed for only about 6x10
17

seconds. There is no way we could ever match in a few universe lifetimes the degree of experimentation that nature has achieved. Therefore the assumption that we may go a step too far has no realistic bearing and is deduced solely from over-active but frenetically anxious imaginations; i.e. science fiction not science fact.


Despite this astronomical but natural experimentation, Arabidopsis has not eliminated all other weeds from ecological niches (far from it) nor generated a species completely resistant to the blandishments of all disease or become super resistant to pests or viruses. But we know that all those traits are already out there in wild populations and in crops; they are not new. It is most probable, given the likely protein combinations that have been tried that the bacterial gene inserted to produce herbicide resistance will have arisen by natural means and simply disappeared. Likewise proteins similar to Bt proteins; but no doubt were found wanting because they didn't deal with the right pest.


Furthermore we also know that there are 250,000 angiosperm species and that nature fiddling as it has with every genome in plants to the same extent has neither generated plants that march across the countryside in serried ranks destroying all before it nor has destroyed or destabilised ecosystems or ruptured life as we know it. Why? Because whatever is produced is naturally constrained by other organisms and it is impossible to construct an organism that provides for every exigency nature and environment throws at it. In criticising GM for moving genes between species with the supposed natural species constraints, opponents simply ignore the experimentation that nature has already carried out but failed to signally manage what opponents imagine GM can do. The biological constraints will limit us in GM terms just as those same constraints have limited biology in the past. As for example expression of a fish gene in plants to try and produce frost resistance miserably failed because it didn't do what it does in fish.


As a final calculation the numbers of different proteins constructed in plants since the origin of plant life itself may be 10
35

. Even larger are the number produced by bacterial cells perhaps someone could estimate?



I have put these figures down they are certainly not new but I think they may be useful in arguments over GM.


Anthony Trewavas