Wednesday, March 5, 2008

Phylogenetic methods talk

Today I gave a 10 min presentation on phylogenetic methods and evolutionary model selection. So I talked about how evolutionary trees are made from genetic sequence data. I think I nailed it pretty well.

After the talk, this guy asked me if you could use this stuff to predict where evolution will take a species in the future. I told him no, unfortunately to predict that you need to know what the environmental pressures will be, and there is a huge random component as well. I went on to tell him that the really interesting thing that you can do with phylogenetics is, fairly accurately, determine the genetic sequence of the last common ancestor of the species you test. The lab I am working in actually recently did that to help refute one of the main anti-evolution arguments posed by creationists. Creationists say that complex systems such as hormone-hormone receptor interactions are too specific to be explainable by evolution. That argument makes sense since hormone receptors are often very specific to the hormone that they bind. It seems that to explain the evolution of such interactions you would have to literally produce both hormone and receptor in the same lineage and it would have to immediately serve a purpose and rise to fixation. If that were true, it would be nearly impossible to do such a thing evolutionarily.

People in my lab sequenced estrogen receptors and estrogen related receptors from a very wide range of organisms to try and get at a very ancient common ancestral hormone receptor to examine it and see what it was like. They then took the sequence generated from the ancestor and grafted it onto yeast cells so they could examine which hormones it was sensitive to. They found that the ancestral hormone receptor was able to bind a variety of ligands including estrogen, which hadn't evolved yet. That showed that you in fact didn't need to evolve hormone and hormone receptor at the same time, that you could start out with a really unspecific hormone receptor that worked with completely different hormones which was eventually taken advantage of evolutionarily to develop into several different, specific hormone receptor-hormone interactions.

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