Chapter 26 – Phylogeny & the Tree of Life

1. Chapter 26 – Phylogeny & the Tree of Life

2. 26.1 • Phylogeny • Evolutionary history of a species or a group of related species • Made by using evidence from systematics • Focuses on classifying organisms & relationships • Uses fossils, morphology, genes, & molecular evidence

3. Taxonomy • Ordered division of organisms into categories • Based on a set of characteristics used to assess similarities & differences

4. BinomialNomenclature • 2 part naming system that consists of the GENUS & the SPECIES • Example: Canisfamiliaris(common dog) • Devoloped by Linnaeus

5. Hierarchical classification of organisms: • DOMAIN • KINGDOM • PHLUM • CLASS • ORDER • FAMILY • GENUS • SPECIES The level of relatedness increases as you move down the list

7. Phylogenetic trees • Used to depict hypotheses about evolutionary relationships • The branches of the trees reflect the hierarchical classifications of groups nested within more inclusive groups

9. 26.2 • Phylogenies are inferred from morphological & molecular data • 1) Homologous structures • Similarities due to shared ancestry (whale’s flipper) • 2) Convergent evolution • When 2 organisms developed similarities as they adapted to similar environmental challenges • Note due to common ancestor • Streamlined bodies of a tuna & dolphin

10. 3) Analogous structures • Structures from convergent evolution • Wings of butterfly & bat • 4) Molecular systematics • Uses DNA to determine evolutionary relationships • The more alike the DNA sequences of 2 organisms, the more closely related they are

11. 26.3 • Building of a phylogenetic tree • A cladogram depicts patterns of shared characteristics among taxa & forms the basis of a PT • A clade (within a tree) is defined as a group of species that includes an ancestral species & all of its descendants

12. A valid clade is monophyletic, signifying that it consists of the ancestor species and all its descendants

13. A paraphyletic grouping consists of an ancestral species and some, but not all, of the descendants

14. A polyphyletic grouping consists of various species that lack a common ancestor

15. 26.4 • The rate of evolution in DNA sequences varies from one part of the genome to another • By comparing the different sequences, one can investigate relationships between groups of organisms that diverged a long time ago

16. DNA that codes for mitochondrial DNA evolves rapidly • Used to explore recent events • DNA that codes for ribosomal RNA changes relatively slowly • Useful for investigating relationships between taxa that diverged hundreds of millions of years ago

17. Molecular clocks • Methods used to measure the absolute time of evolutionary change • Based on the observation that some genes appear to evolve at constant rates

19. Difficulties of molecular clocks • The molecular clock does not run as smoothly as neutral theory predicts • Irregularities result from natural selection in which some DNA changes are favored over others • Estimates of evolutionary divergences older than the fossil record have a high degree of uncertainty • The use of multiple genes may improve estimates

20. 26.6 • New information continues to revise our understanding of the tree of life • Early taxonomists classified all species as either plants or animals • Later, five kingdoms were recognized: Monera (prokaryotes), Protista, Plantae, Fungi, and Animalia • More recently, the three-domain system has been adopted: Bacteria, Archaea, and Eukarya • The three-domain system is supported by data from many sequenced genomes

25. Bacteria & Archaea • Contain prokaryotic organisms • Eukarya • Contain eukaryotic organisms