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Section 7 : Techniques for Studying Evolution and Systematics
Cell and/or tissue organization varies according to each species' phylogenetic position. Different protocols for DNA and protein isolation are required for various taxa. Before DNA can be isolated from a multicellular organism, its tissue must be dissociated into individual cells. This section first discusses isolation of DNA from bacterial, Euglena, yeast, plant, chicken, and human cells, and identifies properties of cell types that must be considered when isolating DNA. Phylogenetic relationships can be determined by comparing key macromolecules. Ribosomal gene sequences from different species can be used to determine evolutionary relatedness. Polymerase chain reaction (PCR) can be used to amplify DNAs from different organisms that contain similar or identical sequences. The next section explains how PCR can amplify similar sequences from a variety of organisms, analyzes PCR products from different species, and demonstrates how small-subunit ribosomal RNA (rRNA) can be used to indicate evolutionary relatedness. Homologous sequences in DNA and protein are hypothesized to be related by descent from a common ancestral sequence. A protein from different organisms may share antigenic epitopes that can assist in determining the relatedness of the proteins. Organisms that are phylogenetically most diverse from one another are least likely to share protein homologies. Finally, the section discusses sequence homology as a tool in phylogenetic studies, explains the differences between antigen and epitope, and describes how antibodies may be used to determine relatedness of different organisms.