Exam7 - Exam 7 Chapter 25Systematics and the Phylogenetic...

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Unformatted text preview: Exam 7 Chapter 25Systematics and the Phylogenetic Revolution 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 tremendous diversity of life, ranging from bacteria to blue whales. Therefore, for generations, scientists have tried to group organisms based on shared characteristics. Biologist name organisms in a systematic way o The classification of organisms Biologists group organisms based on shared characteristics Organisms were 1 st classified by Aristotle over 2000 years ago Similar individuals were eventually classified into units called genera (groups) Many descriptive terms were used in naming until the mid-1700s, when Linnaeus began using a binomial system Taxonomy is the science of classifying living organisms; a group of similar organisms is put into a shared taxon By agreement among taxonomists throughout the world, no two organisms can have the same name, and all names are in LATIN The scientific name of an organism is the same anywhere in the world. The first word of the binomial name is the genus, and is always capitalized. The second word refers to the particular species and is not capitalized. The two words (genus & species) are written in italics. Also, once a genus has been used in the body of a text, it is often abbreviated in later uses. Like T.rex Taxonomic classification is hierarchical, and are composed of (in ascending order): Species Genus Family Order Class Subphylum Phylum Kingdom --- 6 (Max) Domain 3 (Max) o Each level may include anywhere from one to several taxa The names of the taxonomic units higher than the genus level are capitalized but not italicized, or underlined or printed distinctly Scientists construct phylogenies to understand the evolutionary relationships among species o Systematics The field of systematics constructs and studies evolutionary relationships (phylogenies) Page 1 of 29 Exam 7 An evolutionary tree is called PHYLOGENY Descendant species should be relatively similar to their ancestors, and the amount of time since separation should be positively correlated with the degree of genetic divergence . But evolution is not constant in its rate, not unidirectional, and not always divergent Evolution is not unidirectional, as the organisms evolve in one direction and then back the other way Oscillating selection Convergent evolution , in which two species independently evolve to become more similar (often, in a response/adaptation to a similar habitat) Most systematists no longer construct their phylogenetic hypotheses solely on the basis of similarity. Rather, they distinguish that is inherited from the common ancestor of an entire group, and is called ancestral, from similarity that arose within the group, termed derived. Therefore in this method, called cladistics, group, termed derived....
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This note was uploaded on 09/16/2008 for the course BIOL 1722 taught by Professor Jagdeeswaran during the Spring '08 term at North Texas.

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Exam7 - Exam 7 Chapter 25Systematics and the Phylogenetic...

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