1. Cladograms & Dichotomous Keys (Topic 5)
How do scientists figure out which organisms are closely related, and which are distantly related? How do scientists identify organisms?
Cladograms & Dichotomous Keys (Topic 5)

2. Which animals seem most alike? Why?
Morphology: branch of biology that deals with the form and structure of organisms
Which animals seem most alike? Why?

3. Bats and sea lions (mammals) are more closely related to each other than either one is related to a shark (cartilaginous fish) or an eagle ( bird).
Why do you think the sea lion and the shark look so similar even though they are very different species?

4. Convergent Evolution: non-related species develop similar structures due to similar response to environmental pressures (not due to shared ancestry) ; result in analogous structures

5. Divergent Evolution : different structures arise due to specific environmental pressure  new species

6. Observe the following image finches from the Galapagos Islands
Observe the following image finches from the Galapagos Islands. Which type of evolution is this?

7. Observe following image of succulents from two continents that are only distantly related (do NOT share a common ancestor) What type of evolution is this?
Carnegiea gigantea Saguaro from North America
Euphorbia virosa from Africa

8. How are cladograms interpreted?

10. Where would you place a lizard, rat, and goldfish?

12. What are dichotomous keys? Why do we use them?
dicho = Greek root for “two”
tome = Greek root for “to cut”
Tool used to identify new, and unknown organisms
Based on a system of pairs of contrasting statements
Can be developed/used to do any type of classification

14. How can you create a dichotomous key of your own?
Start with a concept map to sort all items/organisms
Convert concept map in to dichotomous statements
Start with one side of concept map – continue statements until you’ve keyed out all organisms on one side. THEN do the other side.
For number of steps in your key, you should end up with 1 less than the number of items your are identifying. (If there are 12 items, there should be 11 steps in your key.)

16. Example of a Dichotomous Key:
1.  Organism is a plant Go to Q2
     Organism is not a plant (animal) Go to Q5
2.  Has no 'true' leaves or roots Bryophyta
     Has leaves and roots Go to Q3
3.  Has no seeds (sporangia) Filicinophyta
     Has seeds Go to Q4 
4.  Has no flowers Coniferophyta
     Has flowers Angiospermophyta
5.  Asymmetrical body plan Porifera
     Symmetrical body plan Go to Q6
6.  Has radial symmetry Cnidaria
     Has bilateral symmetry Go to Q7
7.  Has no anus Platyhelminthes
     Has an anus Go to Q8
8.  Has a segmented body Go to Q9
     Has no visible body segmentation Mollusca
9.  Have an exoskeleton Arthropoda
     Have no exoskeleton Annelida