1. how to make a dichotomous key

2. What is a dichotomous key?
A key for the identification of organisms using paired statements
These statements must be opposites
For example, if the first statement is “has blue eyes,” then the paired statement would be:
Has green/brown/hazel eyes
Does not have blue eyes

3. So how do I make my own dichotomous key?
Make a list of things that you want to classify:
Let’s classify restaurants
Red Lobster
McDonalds
Chili’s
Cracker Barrel
Chick Fil A

4. So how do I make my own dichotomous key?
Group the restaurants into two groups
those with drive-thrus
those without
Write paired statements, one reflecting each group type
those with drive-thrus = “has a drive-thru”
those without drive-thrus = “has no drive-thru”

5. So how do I make my own dichotomous key?
Each statement is like a map. It tells you where to go next.
Read the statement and look at the things that you are trying to classify. How many items match that statement?
If it is one, write the name of the item
If it is more than one, you need another way to divide the group
Go to #(next available number)

6. So how do I make my own dichotomous key?
So in our example, the first statement “has a drive-thru” matches two of the restaurants:
McDonalds
Chick Fil A
So it needs another way to divide them
Go to #2

7. So how do I make my own dichotomous key?
The second statement “has no drive-thru” matches three restaurants:
Red Lobster
Chili’s
Cracker Barrel
So we need another way to divide them:
Go to #3

8. So how do I make my own dichotomous key?
For #2, we need to divide McDonalds and Chick Fil A
serves hamburgers
doesn’t serve hamburgers
Each statement has exactly one match, so we are done with those two restaurants
serves hamburgers = McDonalds
doesn’t serve hamburgers = Chick Fil A

9. So how do I make my own dichotomous key?
For #3, we need to divide Red Lobster, Chili’s, and Cracker Barrel
Serves breakfast
Doesn’t serve breakfast
One statement has exactly one match
Serves breakfast = Cracker Barrel
The other statement has two matches, so we need another category
Doesn’t serve breakfast = Go to #4

10. So how do I make my own dichotomous key?
For #4, we need to separate Chili’s and Red Lobster
Serves whole lobsters= Red Lobster
Doesn’t serve whole lobster = Chili’s
Now all five restaurants are in groups by themselves. Our dichotomous key is complete!

11. I know how to make one.. Now how do I read one?
Pick one of the items that you are trying to classify
ALWAYS start with #1!
Determine which statement matches the item that you are trying to classify, and follow the direction that statement gives you
Once you have classified that item, pick another item until the key is complete!