Saturday, December 10, 2005
Evidence for Todd Wood's Altruistic Genes
- The difference between two species in the same baramin would be mostly due to transposons
- Some AGEs would be physically associated with genes responsible for species-specific traits
- Populations living immediately after the flood were more adaptable than populations living now
These are his specific predictions. He also describes unprocessed pseudogenes, which are unexpressed genes. On page 20, Wood proposes that some unprocessed pseudogenes are latent genes that have not been activated yet, or have been deactivated by AGEs. Barry Hall provides evidence for this in a recent paper (this was actually published before Wood's paper, but Wood did not reference this paper, so it is unlikely that Wood had access to Hall's work, though it does not really matter).
Barry Hall's paper is called Transposable elements as activators of cryptic genes in E. coli. From what I can tell, cryptic genes and unprocessed pseudogenes are two terms for basically the same thing. The only difference I could tell is that the term "unprocessed pseudogene" usually refers to genes that are similar to genes with known function, but are currently unexpressed.
Anyway, a quick summary is that, while biological tradition has held that transposons are essentially purposeless, "selfish", and parasitic in the genome, there are clear examples of transposons which are beneficial, targetted, and environmentally activated.
The main example used is a suite of genes that are used to metabolize a certain type of sugars, called Beta-glucoside sugars. Normally E. Coli is unable to process these sugars, but not because it lacks the genes to do so. The genes are presesnt, but inactive. However, they are also well-preserved by the genome. There are three operons involved -- bgl, cel, and asc, each built from multiple genes. All of these can be activated by insertion sequences placing themselves in the proper places. And, in fact, empirical analysis indicates that these insertions DO NOT occur except under starvation conditions, and then ONLY in the presence of beta-glucoside sugars (arbutin was the one used in the experiments).
So, it seems that transposons are explicitly being used by the cell to enable specified, adaptive responses. It also seems that cells can have suites of genes which are inactive, only to be activated in specific conditions. Wood proposed that this was the case for C3 and C4 photosynthesis -- many plants have both pathways encoded in their genes, but one or the other is switched off by default, enabled by transposons under certain environmental conditions.
But, did God put them there a couple billions years ago so we could find them and so use them?
Transposons are mobile toolkits of genetic functionality, that can be brought in _by the cell_ to restructure function in a beneficial way.
They are important whether or not we ever found them. They are used by the cell as mobile genetic activators/deactivators/restructurers to help cells adapt to changing conditions.
This paper shows the explicit movement of one transposon in direct response to a specific change in the environment in a specifically beneficial way. This is a directed change in the genome in response to stress.