Those of us who have been involved with the debate surrounding intelligent design and evolution for any significant length of time are well acquainted by now with the most fashionable neo-Darwinian model for the origin of novel biological information: gene duplication and divergence. Gene duplications normally arise through a phenomenon known as “unequal cross-over,” which occurs during cell division. This process results in the deletion of a sequence in one strand, and its replacement with a duplicate from its homologous chromosome (meiosis) or its sister chromatid (mitosis). The model of gene duplication and divergence essentially maintains that, following a gene duplication, while one copy of the gene retains its original function, the other copy is freed from selective constraint and is thus free to mutate at a faster rate, and explore sequence space in search of some novel function.
With this background, I wish to conduct a short case study of the evolution of the globin family: heme-containing proteins that are characterized by their incorporation of the globin fold (a series of eight alpha helical segments). The globins are involved in the binding and/or transport of oxygen, the two best-known examples being the reversible oxygen-binders hemoglobin (featured in the diagram above) and myoglobin.
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