Transcript FIGURE 18.1
What is the Linnaean System of Taxonomy? • Levels of taxonomy: Kingdom, Phylum (or Division); Class; Order; Family; Genus and Species – Today, all levels are intended to reflect evolutionary relatedness – Developed by Carolus Linnaeus (mid 1700s), a Swedish botanist • Binomial Nomenclature (Linnaeus, 1758) – Each species receives a unique scientific name in Latin (common names differ by location and change over time) • Latin is a dead language (will not change), and is used internationally – Scientific names always two words (Genus species), always underlined or italicized (versus longer description in Latin); second name not used alone, lower case, often describes location species found or in honor of person • Tomato (pre-Linnaeus): Solanum caule inermi herbaceo, foliis pinnatis incises • Descriptions of Newly Discovered Species – Often identified based on their physical structure (Morphological Species Concept); taxonomists attempt to include genetic comparisons and ecological descriptions also (e.g., habitat) – Holotype and Paratypes: first known specimen and subsequent specimens described in peer-reviewed scientific journal Figures 5-2 and 5-3 Figure 5-4 Figure 5-5 Figure 5-7 Cell Types and Shared Structures • Prokaryotic Cells (Prokaryotes: Eubacteria and Archaea) – Most 1-10 μm; seen in fossil record by 3.5 bya; lack a nucleus and other membrane-bound organelles (DNA free in cell, in nucleoid region) • Eukaryotic Cells (Eukaryotes: Fungi, Protists, Plants, and Animals) – Most 10-100 μm; seen in fossil record by 2.2 bya; have a nucleus and other membrane-bound organelles • All Cells Share (thus common ancestor had …) – Cell (plasma) membrane: a boundary; micelles can form naturally – Ribosomes: composed of proteins and RNA; bacterial ribosomes have a different size and structure than those in eukaryotes – DNA, RNA, and the Genetic Code: bacterial chromosome a simple ring of DNA; in eukaryotes, DNA is packaged with proteins – Other molecules / structures: membrane proteins (ex. ATP, ATP synthase), metabolic enzymes, cytoskeletal tubules and filaments Figures 5-8 and 5-9 How are Phylogenetic Relationships Determined? • Clade: an ancestral species and all of its descendents (a “branch on the Tree of Life”) – Cladistics: systematic analysis of clades and their relationships to other clades; focuses on the evolutionary innovations that define branch points in evolution (synapomorphies: shared, derived traits) • Parsimony: convergence considered more rare than homology; tree that results in fewest number of steps considered most parsimonious • Techniques – Often heavy computer memory requirements for statistical tests (bootstrapping, Monte Carlo simulations, tests of monophyly) • If multiple trees result with equal significance, relationships remain unresolved (a “bush”) • Any single resulting tree still considered a hypothesis; best if consistent with other independent evidence (e.g., the fossil record) – Character states entered for multiple traits (ex. horns present = 1, horns absent = 0); taxa that share more homologies considered more closely related; nucleotide or amino acid sequences often used (eliminates potential bias in choice of characters)