Science Buddies: "Ask an Expert"

I can't seem to find any "old" evolutionary trees (That is, based on morphological date) for the Tree of Life 2 project. Any leads? I would prefer something on the internet, but I can probably work with a book reference... As interesting a fellow as Darwin was, he apparently did not have a talent for drawing, or examples.

Hi wtwwg,

So evolutionary trees are usually called phylogenetic trees. So try searching Google for "classic pylogenetic tree based on morphology". You should be able to find some really nice hand drawn figures from way back before genetics. Here is an especially nice one that I found, and it even has a citation underneath it.

http://www.bio-pro.de/magazin/thema/001 ... ml?lang=en

Let me know if you have any more questions.
Kierstyn

Thank you, I found some do-able ones.

I have another question however,
Almost all the trees I found show the evolution of Orders. So when I search for DNA or protein sequences, would it be acceptable to choose one or two species as a representation? I assume the species within an order have similar sequences for large, common proteins, but some must different. Surely this could be a source of error?

Hi wtwwg,

I think it should be fine to select representative species in each Order. You may find that not all the species in an order have sequence data available. What kind of error are you worried about? If you are worried about the kind of gene (protein) you compare having an effect, try comparing trees made from a couple different genes. Then you will be able to see if that makes a difference.

One thing to keep in mind as you select genes is the function of those genes. For your tree to reflect the true evolutionary relationship between species you need a gene that is evolving very slowly. Then the comparison of the gene will reflect differences between species instead of between individual organisms within a species. When biologists do this they select genes that are under a lot of selective pressure because then the sequences change very little. What kinds of genes do you think would be under high selective pressure? Consider for example a gene that is involved in cell division vs. a gene that is responsible for hair color. Which of these genes would have a sequence that doesn't change very fast? This is also the reason that biologists usually use protein sequence instead of DNA sequences.

Does all of this make sense? Let me know if you have anymore questions.
Kierstyn