Modern Taxonomy Chapter 15, Section 4

What is Taxonomy? The branch of biology involving the identification, naming, and classification of species

The Linnaean System of Classification Carolus Linnaeus (1707-1778) developed a naming system that gave every species a 2-part Latin name and organized them into broader categories “binomial nomenclature” Example: Homo sapiens or Homo sapiens

Linnaean Classification Groups

Taxonomy and Evolution Darwin used Linnaeus’s to show evolutionary relationships → phylogenetic trees The more homologous structures organisms shared, the more closely related they were Today we use molecular evidence, as well as homologies and physical characters to determine ancestry

Phylogenetic Trees & Cladograms

What’s the Difference? Cladogram Phylogenetic tree Both Often include Derived Characters or unique features that unite organisms in a clade Lacks information about the duration of lineages and/or amounts of evolutionary change Phylogenetic tree Indicates evolutionary timescale & degrees of change by the length of lines or numerical differences Both Illustrate a hypothesis about the common ancestry of life

Molecular Phylogeny Comparison of cytochrome c mutations Human Fig. 10.5

Fig. 32.7

How to read a Cladogram/Tree This diagram shows a relationship between 4 relatives. These relatives share a common ancestor at the root of the tree. Note that this diagram is also a timeline. The older organism is at the bottom of the tree. The four descendants at the top of the tree are DIFFERENT species. This is called SPECIATION. DESCENDANTS Stress that cladograms not only serve as a pictorial representation of lineage, but also as a snapshot in time. Be sure to introduce the term SPECIATION. The four descendents are DIFFERENT species. Image courtesy of http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_05

The event that causes the speciation is shown as the fork of the “V”. Branches on the tree represent SPECIATION, the formation of a new species. The event that causes the speciation is shown as the fork of the “V”. Image courtesy of http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_05

Species B and C each have characteristics that are unique only to them. But they also share some part of their history with species A. This shared history is the common ancestor. Image courtesy of http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_05

A CLADE is a group of organisms that come from a common ancestor. If you cut a branch of the tree, you could remove all the organisms that make up a CLADE. Students should be able to decide if a group of organisms form a clade. Image courtesy of http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_06

What is the only thing A and B have in common? Be sure to have students justify their answer to the question. Image courtesy of http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_05

Look at the cladogram at the right Look at the cladogram at the right. What conclusions can be drawn about the relationship between humans and chimps? How many clades are in this cladogram? SEVEN Image courtesy of http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_05

Cladistics (How biologists make cladograms) Organisms in a clade share a derived character Ex: horse & monkey have hair and mammary glands so they are in the same clade If an organism does not share the character that unites a clade, it is placed in broader, inclusive clade Ex: lizard does not have hair or mammary glands, but does have 4 legs and amniotic eggs

Cladistics (cont.) Biologists often use Venn Diagrams to help organize clades, then draw the cladogram The diagram to the right shows 5 different ways to represent a single line of descent in a cladogram

SPECIAL NOTES: Some characters can derive in unrelated clades due to convergent evolution (analogies) The hypothesis with the fewest derivations or steps usually is the accepted hypothesis

Kingdoms and Domains Biologists use the largest taxons to show common ancestry among all of life on Earth (past and present) The number of kingdoms and the formation of domains have changed in response to new discoveries and evidence

Classification of Living Things Domain Bacteria Archaea Eukarya Kingdom Eubacteria Archaebacteria Protista Fungi Plantae Animalia Cell Type Prokaryote Eukaryote Cell Structure Cell walls with peptidoglycan Cell walls without peptidoglycan Some have cell walls of cellulose; some have chloroplasts Cell wall of Chitin Cell walls of cellulose; chloroplasts No cell walls or chloroplasts Number of Cells unicellular Most unicellular; some colonial; some multicellular Most multicellular; Some unicellular multicellular Mode of Nutrition Autotroph or Heterotroph Heterotroph Autotroph Examples Streptococcus; E. coli Halophiles, Methanogens Amoeba, Paramecium, slime molds Mushrooms, yeast Mosses, ferns, flowering plants Sponges, worms, insects, fish