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2011-22_Mole - EVOLUTION(11:704-486 MOLECULAR EVOLUTION...

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E VOLUTION (11:704-486) M OLECULAR E VOLUTION S MOUSE S PRING 2011 1 M OLECULAR E VOLUTION Aims and Methods: With the advent of the molecular revolution, the study of evolution has taken on an increasingly molecular (DNA) flavor. Quite apart from the lure of being ‘modern’, the use of DNA has added a new dimension to evolutionary studies. Molecular Motivations – In many cases, the investigator actually collects the critters, extracts the DNA, and does the analyses that follow. At the end, the data are fed into international data bases for archiving, something like GenBank. Increasingly, people are starting to go straight to GenBank for comparative work, particularly for broad taxonomic coverage - data mining, if you will. For practical work, there are three major things we can do with DNA data. Molecular Markers – For many problems, all we need are molecular markers to provide an analytical tool for traditional problems in evolution. I have talked about using DNA traits to construct phylogenies, though I haven’t said much except that one converts polymorphic nucleotide alternatives to (0, 1) coding. We can also use them in place of allozyme markers. We can also use them for all sorts of population genetic (microevolution) studies for which we have traditionally used other sorts of markers (replacing obvious phenotypic variants, allozymes and other protein markers, chromosome markers, and so on). The idea is simply that ‘a single-gene marker’ is ‘a single-gene marker’, and any piece of DNA will suffice. Molecular Phenotypes – Here, the genes under study are those that have specified impact on the phenotype of the organism. The genes themselves, and their evolution, are the points of interest. I talked about -globin mutants and their genetic consequences, but there are many other examples. The idea is to understand, at a molecular level, what those changes represent. We have even, in some cases, been able to identify the polygenes that underpin some of the continuous phenotypic traits that clearly have a genetic basis. It’s rather nice to have real genes, and not just rely on a model that says the genes are there. The analyses one can do with identifiable genes are an improvement over what can be done with quantitative genetics. Genomic Evolution – There are generalizations one can extract from the evolution of DNA genomes, and there is now emerging a growing interest in what one can say about genomic evolution that is larger than the details of any particular molecule. I talked about gene duplication earlier, but the point here is that we can identify different genes, and show how they are related, and in many cases, develop a phylogenetic tree of the genes themselves, not just of the organisms that possess them. That has turned out to be an interesting exercise, and provides us with an interesting twist on the ‘genes beget genes’ idea.
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