MOUSE – SPRING 2011
Aims and Methods:
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.
– 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.
– 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.
– 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.
– 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.