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Phylogeny and Systematics Chapter 26: (Making “Trees of Life”)

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Presentation on theme: "Phylogeny and Systematics Chapter 26: (Making “Trees of Life”)"— Presentation transcript:

1 Phylogeny and Systematics Chapter 26: (Making “Trees of Life”)

2 Macroevolution studies focus on change that occurs at or above the level of species ▫The origin of taxonomic groups higher than species level How does this occur? Evolution of new traits (novelties) mass extinctions Open adaptive zones (divergent evolution)

3 Currently, scientists use ▫Morphological, biochemical, and molecular comparisons to infer evolutionary relationships  Obtained through fossil studies, DNA technology and current organisms

4 Phylogeny What is phylogeny? The evolutionary history of a group Systematics attempts to reconstruct phylogeny, by analyzing evolutionary relatedness. ▫Use morphological and biochemical similarities Molecular systematics uses DNA, RNA and proteins to infer evolutionary relatedness. Different tools are used to reconstruct phylogenies called phylogentic trees.

5 Molecular systematics

6 Systematics Uses evidence from fossil record and existing organisms to reconstruct phylogeny (Linneaus) Binomial nomenclature Genus species keeps identity of organism universal ▫Other taxa used to classify  Domain, Kingdom, Phylum, Class, Order, Family, Genus, species

7 Taxonomy Linnaeus ordered division of organisms into categories based on a set of characteristics used to assess similarities and differences

8 Linking Classification and Phylogeny Systematists depict evolutionary relationships In branching phylogenetic trees Figure 25.9 Panthera pardus (leopard) Mephitis mephitis (striped skunk) Lutra lutra (European otter) Canis familiaris (domestic dog) Canis lupus (wolf) Panthera Mephitis Lutra Canis FelidaeMustelidaeCanidae Carnivora Order Family Genus Species

9 Each branch point ▫Represents the divergence of two species Leopard Domestic cat Common ancestor

10 “Deeper” branch points ▫Represent progressively greater amounts of divergence Leopard Domestic cat Common ancestor Wolf

11 Cladistics Cladogram is a tree with two way branch points Each branch point represents divergence from common ancestor Each branch is called a clade Clades ▫Can be nested within larger clades, but not all groupings or organisms qualify as clades 3 types of groupings ▫Monophyletic ▫Polyphyletic ▫Paraphyletic

12 Different Types of Clades Monophyletic = single ancestor gave rise to all species in the taxon; ONLY valid clade Polyphyletic = includes numerous types of organisms that lack a common ancestor; not a valid clade Paraphyletic = a grouping that consists of an ancestral species and some, but not all, of the descendants; not a valid clade

13 Grouping 1 MonophyleticParaphyletic Grouping 2 Polyphyletic Grouping 3 Clades

14 Let’s practice…

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16 Making “Trees”: Morphological & molecular homologies similarities based on shared ancestries ▫bone structure ▫DNA sequences beware of analogous structures  convergent evolution

17 Not all Similarities Represent Common Ancestry Homologous structures indicate shared common ancestry ▫Homologous structures are therefore evidence of divergent evolution Analogous structures are similar in function but not in evolutionary history ▫Analogous structures are evidence of convergent evolution It is not always easy to sort homologous from analogous structures

18 RECALL… Convergent evolution occurs when similar environmental pressures and natural selection ▫Produce similar (analogous) adaptations in organisms from different evolutionary lineages Eutherian (placental) Marsupial

19 1. Cladistics = ▫sorts homologous from analogous structures ▫sorts primitive and shared derived characteristics ▫Makes cladograms Making Evolutionary Life Trees: Illustrating Phylogeny

20 The Universal Tree of Life The tree of life is divided into three great clades called domains: ▫Bacteria, Archaea, and Eukarya Figure 25.18 BacteriaEukaryaArchaea 4Symbiosis of chloroplast ancestor with ancestor of green plants 3Symbiosis of mitochondrial ancestor with ancestor of eukaryotes 2Possible fusion of bacterium and archaean, yielding ancestor of eukaryotic cells 1Last common ancestor of all living things 4 3 2 1 1 2 3 4 0 Billion years ago Origin of life

21 A shared primitive character ▫a homologous structure that is shared by all groups we are trying to define A shared derived character ▫A new evolutionary trait unique to a particular clade(s) ▫Making Cladograms Activity Time

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23 A Cladogram What is the shared primitive characteristic? Notochord

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25 Phylograms In a phylogram ▫The length of a branch in a cladogram reflects the number of genetic changes that have taken place in a particular DNA or RNA sequence in that lineage ▫Involves timing  cladograms do NOT! Drosophila Lancelet Amphibian Fish Bird Human Rat Mouse Cenozoic Mesozoic Paleozoic Proterozoic 542 251 65.5 Millions of years ago


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