Ask A Scientist Molecular Biology Archive

name         Maria S.
status       student
age          16

Question -   What types of molecules can be used to determine the evolutionary 
relationship among organisms based on biochemical comparisons?
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Thus far, studies of evolutionary relationships at the molecular level have focused on proteins and nucleic acids. Protein work was undertaken first due to the earlier availability of protein separation technology that could be applied to such studies. As an example, one can observe the location of an alcohol dehydrogenase enzyme in a nondenaturing electrophoresis gel, the position of which will be in large measure a function of the electrical field put across the gel (with respect to degree and time) and the net charge of the enzyme. Mutations in the gene that encodes the enzyme that result in amino acid exchanges that impact the net charge of the enzyme will be detected in the molecule streaming faster or slower in the gel. In this fashion, evolutionary molecular biologists, such as the late Alan Wilson of UC-Berkeley, could compare the evolutionary relationships of wide ranging sets of organisms, and
then compare the molecular data to evolutionary trees based on morphological observations, for example.


Wilson's work itself morphed with the availability of separation technologies 
applicable to the study of nucleic acids, especially once cloning methods rendered 
gene isolations and sequencing a fairly routine matter, within limits. Wilson started 
such work, and it has been extended by others since his passing, by, for example, 
Vince Sarich and colleagues, also located at UC-Berkeley. Evolution, being the study of 
gene mutations, and the results of such mutations, can be directly assessed at the 
genetic level, on a gene by gene basis. With the advent of nucleic acid technologies, 
the evolutionary rates can be assessed not only by mutations that have a visible 
impact, but, as well, mutations that are "silent" in that no difference results in the 
gene product.

One last point to make is that the evolutionary trees based on molecular studies 
frequently reflect what morphological-based studies have reported, at least with 
respect to the big picture. But it is my impression that the molecular studies 
frequently find differences in the details, and are very usefully employed in expanding 
our understanding of the many small changes in an organism's genome that can lead to 
new species, which itself is a very big change.

Donald Silvert
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