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This 11 page Class Notes was uploaded by Alanna Patch on Monday February 8, 2016. The Class Notes belongs to BSC 116 at University of Alabama - Tuscaloosa taught by Dr. Harris in Winter 2016. Since its upload, it has received 84 views. For similar materials see Principles Biology II in Art at University of Alabama - Tuscaloosa.
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Date Created: 02/08/16
Characteristics of Classification Always imposes order Always based on some “reasoning” involving what the classifier deems to be the essential properties of the objects being classified. Often nested in a hierarchy MORE EXCLUSIVE GROUPS INCREASING SPECIFICITY ---------------------------- DomainKingdomPhylumClass Order Family Genus Species ---------------------------- MORE INCLUSIVE GROUPS DECREASING SPECIFICITY Decent with Modification The notion that species evolve over time, and that descent from common ancestors explains why we see the nested pattern that we do. Current thought is that we should make the names of groups reflect the pattern of descent. It also has provided a context for interpreting the different characteristics that we see – not just as more similar or less similar, but as the result of change over time from the same ancestor. 2 Character States Plesiomorphy: an ancestral character Symplesiomorphy: shared ancestral character Apomorphy: a derived character Autapomorphy: unique derived character Synapomorphy: shared derived character Cladograms Diagrams used to show potential relationships between taxa. Any tree represents a HYPOTHESIS of relationships. 3 Any tree may, or may not reflect the actual historical relationships between taxa • Characters can be any features of an organism that are informative. • Must occur within the group of taxa under consideration (ingroup), but not in the outgroup (outgroup is a closely related groups of organisms that does not share any of the distinguishing characteristics of the ingroup) • Should show variation. A character that does not differ between taxa is not informative. • Outgroup: Hypothesized to be closely related to all organisms in the group, but less closely related to any taxa of interest than they are to each other. • Plotting the changes in characters on an alternative tree promotes a different understanding of the evolution of these characters. 4 Parsimony • Parsimony in systematics means choosing the simplest possible explanation for the changes seen in the characters under consideration. • This means that the hypothesis of relationships requiring the fewest evolutionary events, or changes, should be favored over more complicated alternatives. Homoplasy (not homologous character) • The recurrence of similar traits (features) in different groups NOT due to common descent • Sources: o Convergent Evolution – structure that appears similar can evolve in groups which are not closely related o Parallelism – taxa undergo similar changes in commonly derived structures, leading to evolution of similar characters o Character Reversals – the re-establishment of an ancestral state through the loss of an evolutionary novelty 5 Bacteria Data showing that the Bacteria were the first lineage to diverge from the common ancestor of all living organisms suggest that the Archaea and Eukarya are more closely related to each other than they are to the Bacteria. Ribosomal RNA was the molecule used to produce Woese's phylogeny because it evolves slowly and is critical to the function of the ribosome, which serves the same function in all three domains in the tree of life. Binary Fission: [Bacteria reproduce through binary fission] During binary fission, the DNA in the bacterial chromosome is replicated, and one copy is passed to each daughter cell. Although plasmids (small, circular DNA molecules separate from the main bacterial chromosome) are not shown in the figure, any plasmids in a bacterial cell are also replicated and passed to each daughter cell during binary fission. Mutations that arise during DNA replication are one source of genetic variation in bacterial populations. T he rapid reproduction and large sizes of many bacterial populations can yield considerable genetic variation despite a low mutation rate. Offspring produced by sexual reproduction are genetically different from their parents and may be better able to thrive if the environment changes.) Syngamy is the fusion of two gametes to form a diploid zygote. A gametophyte is the multicellular haploid form of a protist that shows alternation of generations. A holdfast attaches spores to surfaces on which they can grow. Phycobilins and other accessory pigments of red algae allow them to absorb the wavelengths of light that penetrate deep water and to use them in photosynthesis. Oomycetes (water molds and their relatives) include both decomposers and the parasites responsible for late potato blight. Chlorophytes (green algae), like green plants, contain both chlorophylls a and b Antibiotic resistance in bacterial populations has followed close upon the heels of the widespread use of antibiotics. As antibioticresistant bacteria thrive and sensitive bacteria die, the proportion of resistant cells in a population increases dramatically. These resistant cells continue to undergo binary fission, resulting in an infection that is difficult to treat. The ability of bacterial populations to evolve resistance requires genetic variation. Mutation is one source of genetic variation. The large population sizes and rapid reproduction of bacterial populations means that even with a low mutation rate, a significant number of mutations are seen in bacterial populations. Some of these mutations contribute to antibiotic resistance. Processes such as conjugation allow for genes to be exchanged among bacteria. Because conjugation can occur between bacterial cells of the same species or of different species, antibiotic resistance sometimes spreads surprisingly easily from one species of bacteria to another. A single R plasmid may have genes that provide resistance to ten or more different antibiotics. This is especially problematic when bacteria that are serious health threats become resistant to multiple antibiotics. For example, methicillinresistant Staphylococcus aureus (MRSA) infections are caused by bacteria that have evolved resistance to most of the antibiotics that were once used to treat staph infections. MRSA is becoming increasingly difficult to treat.
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