Chapter 26 Phylogeny and 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 the two part format of the scientific name of an organism the binomial name consists of genus and species these are always written in a different font italics genus is always capitalized species is always lowercase Ex Homo sapiens this was done by Carolus Linnaeus Hierarchical Classification Linnaeus also introduced the system for grouping species in increasingly broad categories Keep Pipes Clean OF GaS Domain Bacteria Archaea Eukarya Kingdom Phyla Phylum Class Order Family Genera Genus Species figure 26 3 Classification Kingdom Animal Phylum Chordata Class Mammalia Order Primates Family Hominidae Genus Homo 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 represents 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 Which taxon on the tree below is most closely related to taxon c D Which of the following represents the correct order of taxa from the most inclusive to the least inclusive domain kingdom phylum class order family genus Concept 26 2 Phylogenies are inferred from morphological and molecular data Morphological and Molecular Homologies phylogenetic history can be inferred from similarities in homologous structures and genes when compared among organisms homologies can tell us about ancestry generally similar morphology and similar DNA sequences closely related species but beware of analogous structures or molecular sequence a k a 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 cladogram a diagram depicting patterns of shared characteristics among species clade within a cladogram a group of species that includes an ancestral species and all of its descendants if two organisms share a homologous trait they must be related and share common ancestors clades are the basis for our classification system figure 26 11 Monophyletic Grouping figure 26 10a Paraphyletic Grouping figure 26 10b Polyphyletic Grouping made up off an ancestral species and all of its descendants only monophyletic groups qualify as legitimate taxa in cladistics consists of an ancestor and some but not all of that ancestor s descendants grouping that lacks the common ancestor of the species in the group figure 26 10c Shared Ancestral and Shared Derived Characteristics figure 26 11 shared ancestral characteristics homologous structure that predates the branching of a particular clade from other members of that clade shared derived characteristics evolutionary novelty unique to a particular clade example example Is the similarity between the Australian mole and the North American mole due to homology no they are similar due to convergent evolution they are from different areas Concept 26 4 An organism s evolutionary history is documented in its genome Gene Duplication and Gene Families gene duplication the production of multiple copies of a gene within the genome important type of mutation in evolution because it increases the number of genes in the genome Orthologous and Paralogous Pairs orthologous genes genes found in a single copy in the genome diverge only once speciation takes place paralogous genes result from gene duplication more than one copy in the genome can diverge within the clade that carries them figure 26 18 Paralogous Genes figure 21 11b the Globin Gene family has resulted from several gene duplication events figure 21 14 can increase the size of the genome and produce families of genes that carry out a range of functions Choose the pair of paralogous genes from the following list human hemoglobin and chimpanzee hemoglobin wrong because they are homologous genes but in different species orthologous genes not paralogous two alleles of the human hemoglobin gene alleles are different from duplicated genes mouse insulin gene and yeast mating type gene two different rat olfactory receptor genes these are a result of gene duplication events Chapter 27 Prokaryotes 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 some colonial forms range in size from 1 5 micrometers Thiomargarita namibiensis 750micrometers no membrane bound organelles circular chromosomes Prokaryotic cells have a variety of shapes the three most common are spheres cocci rods bacilli and spirals spirilli figure 27 2 Cell surface Structures cell wall maintains cell shape provides physical protection prevents cell from bursting in a hypotonic environment composed of peptidoglycan in bacteria thick for gram positive bacteria thin for gram negative bacteria may also have an outer phospholipid membrane figure 27 3 a capsule a sticky layer of polysaccharide or protein may cover the cell wall of fimbriae and pilli allow prokaryotes to stick to their substrate or other individuals in many prokaryotes figure 27 4 a colony figure 27 5 Gram positive Bacteria have a thick peptidoglycan layer are purple in color after Gram straining shaped like rods alcohol rinse does not remove crystal violet dye has a plasma membrane Streptococcus aureus is an example Gram negative bacteria have a thin peptidoglycan layer have an outer membrane as part of their cell wall structure appear pink after Gram straining alcohol rinse easily removes crystal violet dye also has a plasma membrane Motility motile bacteria move by means of flagellae structurally different from eukaryotic flagella in a heterogeneous environment bacteria exhibit taxis ability to move toward or away from certain stimuli ex positive chemotaxis moving toward a chemical stimulus figure 27 6 less more Gram negative bacteria have
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