Evolutionary trees

Figure 5.3 The deduced evolutionary tree for selected members of the transferrin superfamily, based on comparisons of structures and sequences. The tree combines the transferrins with a number of prokaryotic periplasmic transport proteins. From Bruns et al., 1997. Reproduced by permission of Nature Publishing Group.

L. L. (1994) High resolution of human evolutionary trees with polymorphic microsateUites. Nature. 368,455 57. 

Proteins serving the same function in different species may have different primary structures. The extent of the differences is a measure of their relatedness on the evolutionary tree of life. 

As more sequence information is made available in databases, we can generate evolutionary trees based on a variety of different proteins. Some proteins evolve faster than others, or change faster within one group of species than another. A large protein, with many vari-... 

FIGURE 3-33 Evolutionary tree derived from amino acid sequence comparisons. A bacterial evolutionary tree, based on the sequence divergence observed in the GroEL family of proteins. Also included in this tree (lower right) are the chioropiasts (chi.) of some nonbacteriai species. 

A very readable text describing methods used to analyze protein and nucleic acid sequences. Chapter 5 provides one of the best available descriptions of how evolutionary trees are constructed from sequence data. 

As we will see, the evolutionary tree is bisected into a lower prokaryotic domain and an upper eukaryotic domain. The terms prokaryote and eukaryote refer to the most basic division between cell types. The fundamental difference is that eukaryotic cells contain a membrane-bounded nucleus, whereas prokaryotes do not. The cells of prokaryotes usually lack most of the other membrane-bounded organelles as well. Plants, fungi, and animals are eukaryotes, and bacteria are prokaryotes. The biochemical functions associated with organelles are frequently present in bacteria, but they are usually located on the inner plasma membrane. 

Classical evolutionary tree. All living forms have a common origin, believed to be the ancestral prokaryote. Through a process of evolution some of these prokaryotes changed into other organisms with different characteristics. The evolutionary tree indicates the main pathways of evolution. 

An evolutionary tree can be constructed by comparing the complete sequences of 21 different 16S and l6S-like ribosomal RNAs (rRNAs). The scale bar represents the number of accumulated nucleotide differences (mutations) per sequence position in the rRNAs of the various organisms. (Source From N. R. Pace, G. J. Olsen and C. R. Woese, Cell 5 325, 1986.)... 

Evolutionary trees based on morphology or biochemical differences indicate that all living systems are related through a common evolution. 

I The most important properties of a protein are deter-f mined by the sequence of amino acids in the polypeptide chain. This sequence is called the primary structure of the protein. We know the sequences for thousands of peptides and proteins, largely through the use of methods developed in Fred Sanger s laboratory and first used to determine the sequence of the peptide hormone insulin in 1953. Knowledge of the amino acid sequence is extremely useful in a number of ways (1) it permits comparisons between normal and mutant proteins (see chapter 5) (2) it permits comparisons between comparable proteins in different species and thereby has been instrumental in positioning different organisms on the evolutionary tree (see fig. 1.24) (3) finally and most important, it is a vital piece of information for determining the three-dimensional structure of the protein. 

As surely as intermediates between species are nonexistent, the intermediates between the primary ovum and the first stable fossilized creature are there for us to discover. They will be in the same horizon, only a few thousand years or less apart. Figure 12.3 gives the impression that all species had been washed into the present by a powerful wave so that the times of arrival are only minutely different. The time axis gives one a realistic impression of the awesome speed of appearance of species when compared to the total time of life on earth. The whole colorful world of anthropology that reverberates from fierce battles over what is a common ancestor, what limb should be attached where on which evolutionary tree, all of that fits into a little more than the width... 

Someone will call us back to earth by pointing at journals called Science or Nature and all the evolutionary trees appearing in them that represent the top 5% of the best papers submitted which are replete with evolutionary trees of molecules and creatures. The creme de la cr me... could they be wrong To gain a different perspective one should consider that Agassiz and Owen would have published in those journals Popularity is not synonymous with truth. Fundamentally new concepts always seem to enter from the outside, starting with a single voice and intense unpopularity conceptual science is a lonely affair. 

The evolutionary tree is an illusion created by the successive metamorphosis of clones followed by the rapid development of clone-specific phenotypes. 

The evolutionary tree shows sequential branching of species and proteins as a consequence of chance processes (mutations). 

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