CHAPTER 26 PHYLOGENY AND SYSTEMATICS 1 What are

CHAPTER 26 PHYLOGENY AND SYSTEMATICS 1

�What are the evolutionary relationships between a human, a mushroom, and a flower? �A phylogeny based on DNA data reveals that animals (including humans) and fungi (including mushrooms) are more closely related to each other than to plants. 2

OVERVIEW � Phylogeny is the evolutionary history of a species or group of species. � The discipline of systematics classifies organisms and determines evolutionary relationships of living and extinct organisms. � Systematists use fossil, molecular, and genetic data to infer evolutionary relationships 3

I. Concept 26. 1: Classification A. Taxonomy � The ordered division of organisms into categories based similarities and differences -useful component of systematics B. Binomial Nomenclature (two word name) 1. First proposed by Carolus Linnaeus in 18 th century 2. Two main characteristics: a. Each species has a two-part name. b. Species are organized hierarchically into broader and broader groups of organisms. 4

3. The first part of the name is the genus. 4. The second part, called the specific epithet, is unique for each species within the genus. 5. Ex: Human—Homo sapiens which means wise man C. Hierarchical Classification 1. Groups species into increasingly broad taxonomic categories 2. Taxonomic groups from broad to narrow are: domain, kingdom, phylum, class, order, family, genus, and species 3. A taxonomic unit at any level of hierarchy is called a taxon 5

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D. Phylogenetic Tree 1. Diagram used to show the evolutionary history of a group of organisms 2. Can provide important information about similar characteristics in closely related species 7

II. Concept 26. 2: Morphological and Molecular Data A. To infer relationships, systematists gather information about morphologies, genes, and biochemistry of living organisms B. Organisms with similar morphologies or DNA sequences are likely to be more closely related than organisms with different structures or sequences C. When constructing a phylogeny, systematists need to distinguish whether a similarity is the result of homology or analogy 1. Homology is similarity due to shared ancestry � Ex: bones of a whale’s flipper and a tiger’s paw 8

2. Analogy is similarity due to convergent evolution � Convergent evolution occurs when two organisms developed similarities as they adapted to similar environmental challenges—not because they evolved from a common ancestor � Ex: wing of a butterfly is analogous to wing of a bat because both are adaptations for flight 3. Analogous structures or molecular sequences that evolved independently are also called homoplasies 4. Homology can be distinguished from analogy by comparing fossil evidence and the degree of complexity 5. The more complex two similar structures are, the more likely it is that they are homologous 9

D. Molecular systematics uses DNA and other molecular data to determine evolutionary relationships. � The more alike the DNA sequences of two organisms, the more closely related they are evolutionarily. 10

III. Concept 26. 3: Constructing Phylogenetic Trees A. Cladistics 1. Cladistics groups organisms by common descent 2. Once homologous characters have been identified, they can be used to infer a phylogeny 3. A cladogram depicts patterns of shared characteristics among taxa and forms the basis of a phylogenetic tree 4. A clade is a group of species that includes an ancestral species and all its descendants � Not all groupings of organisms qualify as clades 5. A valid clade is monophyletic, signifying that it consists of the ancestor species and all its descendants 11

MONOPHYLETIC GROUP (CLADE) � Group I, consisting of 3 species (A, B, C) and their common ancestor (1), is a clade, also called a monophyletic group. � A monophyletic group consists of an ancestral species and all of its descendants 12 1

PARAPHYLETIC GROUP � Group II is paraphyletic. � A paraphyletic grouping consists of an ancestral species and some, but not all, of the descendants. � In this case Group II consists of an ancestral species (2) and some of its descendants (species D, E, F) but not all of them (missing species G). 13 2

POLYPHYLETIC GROUP � Group III is polyphyletic. � A polyphyletic grouping consists of various species that lack a common ancestor � In this case, species D, E, F, and G share common ancestor (2), but species C has a different ancestor (1). 14 1 2

B. Shared Ancestral and Shared Derived Characters 1. A shared ancestral character is found not only in the clade being analyzed but also in older clades � Ex: Backbone in vertebrates 2. A shared derived character is unique to a particular clade. �Ex: Hair in mammals 3. A character can be both ancestral and derived, depending on the context 4. When inferring evolutionary relationships, it is useful to know in which clade a shared derived character first appeared 15

Phylogenetic Tree 16

IV. Concept 26. 4: Genome Documentation(Not on exam) A. Comparing nucleic acids or other molecules to infer relatedness is a valuable tool for tracing organisms’ evolutionary history B. DNA that codes for ribosomal RNA changes relatively slowly and is useful for investigating branching points hundreds of millions of years ago C. Mitochondrial (mt)DNA evolves rapidly and can be used to explore recent evolutionary events 17

V. Concept 26. 5: Molecular Clocks(not on exam) � Molecular clocks are methods used to measure the absolute time of evolutionary change based on the observation that some genes and other regions of the genome appear to evolve at constant rates. 18

VI. Concept 26. 6: Three-Domain System A. Supported by data from many sequenced genomes B. A Comparison of the Three Domains of Life Characteristics Bacteria Archaea Eukarya Nuclear Envelope No No Yes Membrane-enclosed organelles No No Yes Introns No Yes Histone proteins associated with DNA No Yes Circular Chromosome Yes No 19

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You should now be able to: 1. 2. 3. 21 The taxonomic categories and how they indicate relatedness How systematics is used to develop phylogenetic trees The three domains of life including their similarities and their differences