1. CHAPTER 17 – CLASSIFICATION OF ORGANiSMS
17-1: Biodiversity
17-2: Systematics
17-3: Modern Classification

2. 17-1: Biodiversity
Biologists have named and classified almost 2 million species
Over time, scientists have created various systems of classification to organize their knowledge of the tremendous # of species
each system places species into categories based on particular characteristics

3. Classifying organisms
Biodiversity
The variety of organisms considered at all levels from populations to ecosystems
Terry Erwin (1980s)
Catalogued insect species in tropical rain forest
Found over 1000 species in only 19 trees

4. Classifying organisms
Every year, biologists discover 1000s of new species and seek to classify them in a meaningful way
Ex. – the pangolin
Grouped with lizards + crocodiles due to scales?
Grouped with animals that use sticky tongues to eat ants?

5. Taxonomy
Taxonomy
The science of describing, naming, + classifying organisms
Taxon
Any particular group within a taxonomic system

6. Taxonomy Aristotle Classified organisms in 2 taxa: Plants
Grouped them based on stem differences
Animals
Grouped them based on where they lived:
Land, water, or air

7. Taxonomy Aristotle’s system was inadequate
Common names were not useful either
Ex. Robin or Fir tree
Vary from place to place
More than one common name
Don’t accurately define a species (i.e. Jellyfish)

8. The linnaean system Carolus Linnaeus
System that grouped organisms into hierarchical categories according to their form + structure (morphology)
System had 7 levels

9. Levels of classification
Kingdom
Phylum
Class
Order
Family
Genus
Species

10. Binomial nomenclature
Linnaeus gave an organism a species name, or scientific name, with two parts:
Genus
Species identifier
Examples:
Homo sapiens
Thamnophis melanogaster
Drosophila melanogaster
Binomial nomenclature

11. Your classification Kingdom Animalia Phylum Chordata
Subphylum Vertebrata
Class Mammalia
Order Primates
Family Hominidae
Genus Homo
Species sapiens

12. Binomial nomenclature
Subspecies
Species that live in different geographic areas
Example:
Terrapene carolina triungui

13. Classification video

14. 17-2: Systematics
Modern biologists consider not only the VISIBLE SIMILARITIES but also similarities in:
Embryos
Chromosomes
Proteins
DNA
Systematics
Goal is to classify organisms in terms of their natural relationships
organize in context of evolution

15. phylogenetics
Systematic taxonomists agree that an organism’s classification should reflect PHYLOGENY (evolutionary history)
Phylogenetics
The analysis of the evolutionary or ancestral relationships among taxa.

16. phylogenetics Use comparisons to classify: Living species vs. fossils
Embryonic development + gene expression
Chromosomes or macromolecules (DNA/RNA)

17. phylogenetics Represent hypotheses by a phylogenetic tree (diagram)
Branching pattern indicates how closely related a subset of taxa are thought to be
May be revised with new discoveries or evidence

18. Evidence of shared ancestry
Biologists use fossils as important clues for the timing of evolutionary changes + divergence
The fossil record my lack evidence…
May also compare…
Homologous features (jaws of pangolin + dogs)
Analogous features (scales of snakes + pangolin)
Embryology (amnion)
The greater the # of features shared by organisms, the more closely related the organisms are

19. Cladistics 1966 – Willi Hennig Cladistics
A system of phylogenetic analysis that uses shared + derived characters as the only criteria for grouping taxa
Shared – feature that all members of a group have in common
Ex. Hair in mammals or feathers in birds
Derived – feature that evolved only within the group

20. Cladistics
Cladistics assume that organisms share one or more derived characters
Probably inherited them from an common ancestor
Group known as a “clade”
Includes its ancestors + all descendants
No other categories (i.e. order, class, etc..)
Creates a cladogram to show their hypothesis

21. Example - A cladogram

22. Constructing a cladogram
Out-group
Organism that is only distantly related to the other organisms
Acts as a starting point for comparisons

23. Molecular cladistics
Biologist can count the shared, derived amino acids at each position in a protein to make a cladogram

24. Molecular cladistics “Molecular Clock”
A tool for estimating the sequence of past evolutionary events
Suggests that the greater the differences between a pair of sequences, the longer ago those two sequences diverged from a common ancestor

25. chromosomes
If two species have the same banding pattern in regions of similar chromosomes, the regions are likely to have been inherited from a single chromosome in the last common ancestor of the two species

26. Putting it all together
To classify an organism and represent its systematics in an evolutionary context, biologists use many types of information to build and revise phylogenetic models:
Physical features
Embryos
Genes in nucleus
Mitochondrial DNA
Ribosomal RNA

27. 17-3: modern classification
Taxonomists have revised two Linnaean-inspired categories
Domains
Kingdoms

28. The tree of life
Based on cell types, scientists can divide all life into two groups:
Eukaryotes
Prokaryotes
Carl Woese
Proposed major revision of 6 kingdom system
Compared rRNA sequences of different organisms and grouped them according to their similarities

30. Three domains of life Insights from rRNA analyses:
Data is consistent with hypotheses that all living organisms inherited their rRNA genes from ancient organisms or form of life
All living things can be grouped into 1 of the 3 domains: BACTERIA, ARCHAEA, or EUKARYA
Species in domain ARCHAEA are greatly different than bacteria

31. Domain bacteria Small, single-celled prokaryotes Have cell walls
Contain peptidoglycan
Reproduce by binary fission
One circular chromosome

32. Domain archaea Have distinctive cell membranes
Made of hydrocarbons, not fatty acids
Some are autotrophic (chemosynthesis)
May inhabit harsh environments

33. Domain eukarya Consists of eukaryotic organisms
Includes plants, animals, fungi, + some single-celled organisms

34. Six kingdoms The 6 kingdoms are more of a traditional taxonomic system
Eubacteria
Archaebacteria
Protista
Fungi
Plantae
Animalia