1. Classification and Diversity
The Linnaean System of Classification, Dichotomous Keys, Cladograms, and Molecular Clocks

2. There are tons of living organisms in the world
There are tons of living organisms in the world. New organisms are still being found and identified all the time! How do we keep up with all of them? Classification is the arrangement of organisms into orderly groups based on their similarities. Classification is also known as taxonomy. Taxonomists are scientists that identify & name organisms.

3. Taxon: a group of organisms in a classification system.
Where did the current system of classification come from?

4. Classified organisms by their structure
Carolus Linnaeus 1707 – 1778
18th century taxonomist
Classified organisms by their structure
Developed naming system still used today
Called the “Father of Taxonomy”
Developed the modern system of naming known as binomial nomenclature: What is that?
Two-word name (Genus & species)
Genus?
Species?

5. Which TWO are more closely related? How do you know this?
Binomial Nomenclature
Which TWO are more closely related? How do you know this?

6. 7 Levels of the Linnaean Classification System
Kingdom
Phylum
Class
Order
Family
Genus
Species

7. Notice how each level gets more and more specific as we move from kingdom to species.

8. Limitations to the Linnaean System
-Created before technology allowed us to view organisms at the molecular level. How has the study of genetics helped us to further classify organisms?
-Example: How have molecular biologists been able to correct misconceptions about the classification of giant pandas, raccoons, and red pandas? (Hint: see p. 521)

9. Dichotomous Key
Used to identify organisms
Characteristics given in pairs
Read both characteristics and either go to another set of characteristics OR identify the organism

10. Example of a Dichotomous Key
1a Tentacles present – Go to 2
1b Tentacles absent
2a Eight Tentacles – Octopus
2b More than 8 tentacles – 3
3a Tentacles hang down – go to 4
3b Tentacles upright–Sea Anemone
4a Balloon-shaped body–Jellyfish
4b Body NOT balloon-shaped - 5

11. Classification is based on evolutionary relationships.
To classify species according to how they are related, scientists must look at more than just their physical characteristics. Why?
Modern classification is based on figuring out evolutionary relationships using evidence from living species, the fossil record, and molecular data.
The evolutionary history for a group of species is called a phylogeny.

12. Cladogram
Diagram showing how organisms are related based on shared, derived characteristics such as feathers, hair, or scales. It proposes how species may be related to each other through common ancestors.

14. How in the world do I read a cladogram?
3 Main Features: Derived Characters, Nodes, and Identifying Clades
Derived Characters: Groups of species are placed in order by the derived characters that have added up in their lineage over time; they are placed in order from earliest ancestor to common organism. Shown as hash marks between the branches of a cladogram. All species ABOVE the hash marks share the derived character denoted by the hash mark.
Nodes: Location where a branch splits. Represent the most recent common ancestor shared by a clade.
Identifying Clades: A clade is a group of species that shares a common ancestor. Also, use the “snip rule.” What is this? (Hint: see p. 526).

15. Critical Thinking:
Why does DNA often have the “last word” when scientists are constructing evolutionary relationships?
Shared or identical sequences of DNA is hard proof of common ancestry, whereas shared traits or similar characteristics can be the result of convergent evolution.

16. Molecular Clocks
DNA changes slightly each time it is passed on from generation to generation.

17. -In the 1960s, Linus Pauling and Emile Zuckerkandl compared amino acid sequences in lots of different species.
-They found that the more distantly related two organisms were, the more differences existed in their hemoglobin (where the studied amino acid sequences are located).
-Used this to calculate a mutation rate for the hemoglobin protein.
-Molecular clocks are models that use mutation rates to measure evolutionary time.
-How do these work?
-The more time that has passed since two species have diverged from a common ancestor, the more mutations will have built up in each lineage, and the more different the two species will be at the molecular level.

18. Linking Molecular Data
With Real Time

19. Mitochondrial DNA DNA found only in mitochondria.
Why is mtDNA a good molecular clock for closely related species? (Hint: see p. 532).

20. Ribosomal RNA
RNA that is in the ribosome and guides the translation of mRNA into a protein.
How is rRNA useful for studying distantly related species? (Hint: see p. 532).