1. KEY CONCEPT Modern classification is based on evolutionary relationships.

2. Physical similarities are not always the result of close relationships.
Genetic similarities more accurately show evolutionary relationships.

3. PHYLOGENY
Biologists group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities.
Phylogeny = the study of evolutionary relationships among organisms.

4. Phylogenetic Tree

5. Phylogenetic trees are usually based on a combination of these lines of evidence:
    Fossil record
    Morphology (structure)
    Embryological patterns of development
    Chromosomes and DNA

6. PHYLOGENY Classification using Cladograms
Cladograms are diagrams that show the evolutionary relationships among a group of organisms.
A phylogenetic tree is a specific type of cladogram where the branch lengths are proportional to the predicted or hypothetical evolutionary time between organisms or sequences. Cladograms are branched diagrams, similar in appearance to family trees, that illustrate patterns of relatedness where the branch lengths are not necessarily proportional to the evolutionary time between related organisms or sequences.

7. PHYLOGENY Example of a cladogram A B C D E F
Speciation: formation of two
new species from one
Clade or
lineage
TIME
Definition of Clade: A group of organisms, such as a species, whose members share homologous features derived from a common ancestor.
The American Heritage® Dictionary of the English Language, Third Edition copyright © 1992 by Houghton Mifflin Company. Electronic version licensed from INSO Corporation; further reproduction and distribution restricted in accordance with the Copyright Law of the United States. All rights reserved.

8. CLADOGRAMS
This cladogram shows the evolutionary relationship among several vertebrates.
Fur &
Mammary
Glands
Jaws
Lungs
Claws
or Nails
Feathers
Hagfish
Fish
Frog
Lizard
Pigeon
Mouse
Chimp

9. CLADOGRAM
Fur &
Mammary
Glands
Jaws
Lungs
Claws
or Nails
Feathers
Hagfish
Fish
Frog
Lizard
Pigeon
Mouse
Chimp
Characteristics listed below the line are called derived characters (traits).

10. CLADOGRAM
Fur &
Mammary
Glands
Jaws
Lungs
Claws
or Nails
Feathers
Hagfish
Fish
Frog
Lizard
Pigeon
Mouse
Chimp
Do frogs have mammary glands?
Do hagfish have jaws?
When the derived character is above an organism, the organism lacks that derived character.

11. 3. CLADOGRAM
Fur &
Mammary
Glands
Jaws
Lungs
Claws
or Nails
Feathers
Hagfish
Fish
Frog
Lizard
Pigeon
Mouse
Chimp
Do pigeons have claws or nails?
Do lizards have jaws?
When the derived character is below the organism, the organism possesses that derived character.

12. copyright cmassengale
Primate Cladogram
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15. The Dichotomous Key
Device for easily and quickly identifying an unknown organism.
The dichotomous key is the most widely used type in biological sciences.
The user is presented with a sequence of choices between two statements, couplets, based on characteristics of the organism. By always making the correct choice, the name of the organism will be revealed.

16. copyright cmassengale
Dichotomous Keying
Used to identify organisms
Characteristics given in pairs
Read both characteristics and either go to another set of characteristics OR identify the organism
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17. Example of Dichotomous Key
1a Tentacles present – Go to 2
1b Tentacles absent – Go to 3
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
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18. A. one pair of wings
B. Two pairs of wings