Teaching Molecular Evolution in School
Heidelberg, 28 - 30 September 2009
“I think...”. This 1837 sketch from Charles Darwin‘s first notebook on transmutation of species is likely to be his first diagram of an evolutionary tree (on view at the the Museum of Natural History in Manhattan. image adapted from Wikimedia Commons, user:Jrockley)
Biological evolution and natural selection are the fundamental processes determining biological organisms. 2009 marks the 250th celebration of the publication of Darwin’s On the Origin of Species where he laid down his theory of evolution and the mechanism of natural selection. Although Charles Darwin’s name is associated with evolution, he was not alone in putting forward the idea that living species are the product of a gradual process of change driven by natural selection.
In the first scientific seminar Michael Knop (EMBL) asked the question: What is evolution? reflecting on the convergence of Darwin’s and Gregor Mendel’s ideas, which provided the evidence for a mechanism for the exchange of traits, and later mathematical approaches which led to the consolidation of neo-Darwinism or modern evolutionary synthesis. Michael re-examining examples of selection such as industrial melanism in moths, and compared the apparent costs and payoffs of sexual and asexual reproduction which create problems for evolutionary theory. As well as studying the biology of yeast reproduction, Michael’s group use computer simulations of virtual organisms to look at the behaviour and evolution of yeast populations under different conditions, in order to understand when and why sex is important, how it evolved and its consequences. As well as being an important evolutionary model organism, yeast can also be used as a powerful tool in the laboratory. Snaps shots from experiments: molecular evolution in yeast took a closer look at a technique called DNA Shuffling used by the Knop Group to improve the brightness of a fluorescent protein, mKeima, through molecular evolution: harnessing the principals of evolution in the lab.
The first hands-on practical activity, Investigating Plant Evolution Kit, devised by the University of Reading’s National Centre for Biotechnology Education, provides an excellent practical example of how genetic differences between species can be used to determine evolutionary relationships. The kit enables students to determine the relatedness of different plant species by PCR amplification and comparing cpDNA from a specific highly variable region. After running the PCR products on agarose gels, the molecular profiles obtained for each plant can be compared to identify possible evolutionary relationships.
The questions that most interest Detlev Arendt’s Group concern the evolution of the brain: How did our central nervous system come into existence? What did it initially look like and how did it function? To find answers, they are trying to reconstruct the brain of the Urbilateria: the hypothetical ancestor of all animals that are ‘bilaterally symmetric’ — including all worms, insects and vertebrates. This creature lived over 600 million years ago, but almost nothing is known about it as it has left no fossils. Detlev described his group’s work on comparing the development of the marine rag worm Platynereis to that of other species is providing molecular evidence for how the brain of the Urbilateria would have looked like.
We need muscles to breath, eat and walk. The variations in an organism’s muscle proteins reflects its physiological adaptation to different environments, but they originate as random DNA mutations. Such mutation events, if favourable, persist through the natural selection process and contribute to the evolution of species — with new specialized functions. In the third hands-on activity, the teachers used the Protein Profiler Module of the Bio-Rad Comparative Proteomics series to compare the proteomes found in muscle tissue from different fish species. Based on their experimental results, they were able to construct phylogenetic trees showing the possible evolutionary relationships between the different species.
Taking the oxygen-carrier molecule haemoglobin as an example, Adian Budd and Francesca Diella (EMBL Heidelberg) looked at how mutations in the DNA cause changes in the amino acid sequence of a protein, altering its structure and, in turn, affecting its function. In Using bioinformatics to look at protein evolution they followed the example of sickle cell anemia where a single mutation in the beta globin gene leads to a single mistake in the amino acid sequence, which can have major consequences for the haemoglobin protein and for the health of that individual.
Trees have been used in biology to illustrate the branching ancestry between animals and plants since Darwin himself drew a simple sketch of relationships between species in 1837. Physical traits of organisms were used to order animals (and plants) into kingdoms, phyla, class, order, family, genus and species, and trees illustrated the divergence over time and relationships between the organisms. However, single-celled organisms like bacteria which lacked visible physical traits were not placed in an order and were even thought to be of little importance. In the 1960’s all this changed with the invention of DNA sequencing, allowing scientists to construct the first molecular trees of organisms based on their genetic relatedness. New techniques now reveal that single-cell organisms regularly shared genes with each other (in a process known as horizontal gene transfer), calling into question whether relationships between organisms should be illustrated as a web not a tree. Chris Creevey talked about the concept of phylogenetic trees, as they are still presented today in biology textbooks, and the new ways in which scientists use similar concepts to present the mass of data emerging from genomic sequencing.
The LearningLAB closed with a presentation of activities that can be imported directly into the classroom. Philipp Gebhardt presented his “artificial ribosome” which illustrates virtually the information flow from DNA to protein sequences. This classroom kit demonstrates the effect of a mutation at the DNA level, and its consequences for the resulting protein.