1. Making a Dichotomous Key

2. Example of Dichotomous Key
1a Tentacles present – Go to 2
1b Tentacles absent – Go to 6
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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3. Rule 1
Each step is made of two parts labeled 1A and 1B, then 2A and 2B, and so on.
1a. Bean round ………………………….Garbanzo bean
1b. Bean elliptical or oblong……………………Go to 2
2a.Bean white……………………………White northern
2b.Bean has dark pigments……………………..Go to 3

4. Rule 2
When you start a key, your first step is to try and break the objects into two groups about the same size

5. Rule 3
Each step either identifies a specimen, or gives directions of the next step to go to.
2a.Bean white……………………………..White northern
2b.Bean has dark pigments…………………….…Go to 3
3a.Bean evenly pigmented……………………….Go to 4
3b.Bean pigmentation mottled……………Pinto bean

6. Rule 4
At each step you choose one of the choices, not both.

7. Rule 5
When you are writing a set of choices, it is better to use a present/absent choice because it is more inclusive.
Use characteristics that are definite.