Chapter 26 Phylogeny the Tree of Life Phylogeny the evolutionary history of a species or group of related species Systematics an analytical approach to understanding the diversity and relationships of organisms Concept 26 1 Phylogenies show evolutionary relationships Taxonomy the ordered division of organisms into categories based on a set of characteristics used to assess similarities and differences Binomial Nomenclature Carolus Linnaeus invented the way that we classify organisms The two part format of the scientific name of an organism The binomial name consists of genus and species o These are always written in a different font e g italics o Genus is always capitalized species is always lowercase Example Homo sapiens Hierarchical Classification Linnaeus also introduced the system for grouping species in increasingly broad categories Figure 26 3 o King Philip Came Over from Greece Singing kingdom phylum class order family genus and species Classification o Kingdom Animalia o Phylum Chordata o Class Mammalia o Order Primates o Family Hominidae o Genus Homo o Species H sapiens Linking Classification and Phylogeny Systematists depict evolutionary relationships in branching phylogenetic trees Each branch point node represents the divergence of two species Deeper branch points represent greater amounts of divergence Lines represent lineages Figure 26 4 Interpreting Phylogenetic Trees Interior nodes represent common ancestors Taxa at tips represent living species groups Rotating around any node leaves a phylogeny unchanged Concept 26 2 Phylogenies are inferred from morphological and molecular data Morphological and Molecular Homologies Phylogenetic history can be inferred from similarities in homologous structure and genes when compared among organisms Generally similar morphology and similar DNA sequences closely related species But beware of analogous structures or molecular sequences aka homoplasies Similarity may be due to convergent evolution analogy not shared ancestry homology Concept 26 3 Shared characters are used to construct phylogenetic trees Cladistics species Cladogram a diagram depicting patterns of shared characteristics among Clade within a cladogram a group of species that includes an ancestral species and all of its descendants Figure 26 11 Monophyletic Grouping Made up of an ancestral species and all of its descendants Only monophyletic groups qualify as legitimate taxa in cladistics Paraphyletic Grouping Consists of an ancestor and some but not all of that ancestor s descendants Figure 26 10b Polyphyletic Grouping Grouping that lacks the common ancestor of the species in the group Figure 26 10c Shared Ancestral and Shared Derived Characteristics Shared ancestral characteristic homologous structure that predates the branching of a particular clade from other members of that clade Shared derived characteristic evolutionary novelty unique to a particular clade Figure 26 11 Concept 26 4 An organism s evolutionary history is documented in its genome Gene Duplications and Gene Families Gene duplication the production of multiple copies of a gene within the genome o Important type of mutation in evolution because it increases the number of genes in the genome Orthologous and Paralogous genes Orthologous genes genes found in a single copy in the genome o Diverge only once speciation takes place o Figure 26 18 Paralogous genes result from gene duplication o More than one copy in the genome o Can diverge within the clade that carries them o Figure 21 11b o Figure 21 14 The globin gene family has resulted from several gene duplication events Clicker Q Choose the pair of paralogous genes from the following list o Human a hemoglobin and chimpanzee a hemoglobin Homologous genes any differences come from speciation so it is orthologous gene o Two alleles of the human a hemoglobin gene Alleles are different varieties of the same gene o Mouse insulin gene and yeast mating type gene In no way homologous o Two different rat olfactory receptor genes Chapter 27 Prokaryotes Clicker Q One thing that E coli and other bacteria have in common with eukaryotes is the presence of ribosomes Concept 27 1 Structural and functional adaptations contribute to prokaryotic success Prokaryotes are unicellular o Some colonial forms Range in size from 1 5 micrometers o Thiomargarita namibiensis is a prokaryote that is longer than the average site It is 750 micrometers No membrane bound organelles no mitochondria chloroplast nucleus etc Circular chromosomes Prokaryotic cells have a variety of shapes o The three most common are spheres cocci rods bacilli and spirals spirilli o Figure 27 2 Cell Surface Structures Cell wall o Maintains cell shape provides physical protection prevents cell from bursting in a hypotonic environment o Composed of peptidoglycan in bacteria o May also have an outer phospholipid membrane o Figure 27 3 A capsule a sticky layer of polysaccharide or protein may cover the cell wall Fimbriae and pilli allow prokaryotes to stick to their substrate or other individuals in a colony They increase the surface area of the prokaryote of many prokaryotes o Figure 27 4 o Figure 27 5 Motility o Motile bacteria move by means of flagellae Structurally different from eukaryotic flagella o In a heterogeneous environment bacteria exhibit taxis ability to move toward or away from certain stimuli Positive chemotaxis moving toward a chemical stimulus Negative chemotaxis moving away from a chemical stimulus o Figure 27 6 Clicker Q Gram negative bacteria have less peptidoglycan than gram positive cells and their cell walls are more complex structurally Clicker Q Groups of Staphylococcus aureus look like clusters of grapes Clicker Q Bacteria have a single chromosome Internal Organization Prokaryotes do not have membrane bound organelles ex mitochondria Some do have specialized membranes that perform metabolic functions Figure 27 7 Genomic Organization Prokaryotic chromosome circular DNA found in the nucleoid region o Not within a nucleus Plasmid smaller circular DNA rings o Additional genes not always necessary for basic survival o Example antibiotic resistance Figure 27 8 Reproduction Prokaryotes reproduce by a process called binary fission o Can divide every 1 3 hours o Form of asexual reproduction that produces genetically identical daughter cells Concept 27 2 Rapid reproduction mutation and genetic recombination promote genetic diversity in prokaryotes Bacteria reproduce asexually leading to
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