rav65819_ch23_453-470

rav65819_ch23_453-470 - ; chapter 23 Systematics and the...

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Systematics and the Phylogenetic Revolution introduction ALL ORGANISMS SHARE MANY biological characteristics.They are composed of one or more cells, carry out metabolism and transfer energy with ATP, and encode hereditary information in DNA. Yet, there is also a tremendous diversity of life, ranging from bacteria and amoebas to blue whales and sequoia trees. For generations, biologists have tried to group organisms based on shared characteristics. The most meaningful groupings are based on the study of evolutionary relationships among organisms. New methods for constructing evolutionary trees and a sea of molecular sequence data are leading to improved evolutionary hypotheses to explain life’s diversification. concept outline 23.4 Phylogenetics and Comparative Biology 23.1 Systematics Branching diagrams depict evolutionary relationships Similarity may not accurately predict evolutionary relationships 23.2 Cladistics The cladistic method requires that character variation be identifed as ancestral or derived Homoplasy complicates cladistic analysis Other phylogenetic methods work better than cladistics in some situations 23.3 Systematics and Classi±cation The phylogenetic species concept (PSC) Focuses on shared derived characters The PSC also has drawbacks Homologous Features are derived From the same ancestral source; homoplastic Features are not Complex characters evolve through a sequence oF evolutionary changes Phylogenetic methods can be used to distinguish between competing hypotheses Phylogenetics help explain species diversifcation
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23.5 Phylogenetics and Disease Evolution HIV has evolved from a simian viral counterpart Phylogenetic analysis identiFes the path of transmission Phylogenies can be used to track the evolution of AIDS among individuals 453 rav65819_ch23_453-470.indd 453 rav65819_ch23_453-470.indd 453 12/7/06 9:39:22 AM 12/7/06 9:39:22 AM 23.1 Systematics One of the great challenges of modern science is to understand the history of ancestor–descendant relationships that unites all forms of life on Earth, from the earliest single-celled organisms to the complex organisms we see around us today. If the fossil record were perfect, we could trace the evolutionary history of species and examine how each arose and proliferated; however, as discussed in chapter 21, the fossil record is far from complete. Although it answers many questions about life’s diversification, it leaves many others unsettled. Consequently, scientists must rely on other types of evidence to establish the best hypothesis of evolutionary relationships. Bear in mind that the outcomes of such studies are hypotheses, and as such, they require further testing. All hypotheses may be disproven by new data, leading to the formation of better, more accurate scientific ideas. The reconstruction and study of evolutionary relationships is called
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rav65819_ch23_453-470 - ; chapter 23 Systematics and the...

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