All dogs descend from the gray wolf, but after 15,000 years of domestication, they have been bred into hundreds of different varieties since then, from the diminutive Chihuahua to the large St. Bernard. It is quite simple for even an untrained person to tell these dogs apart based on their inbred characteristics, making dogs a good animal to classify with a dichotomous key. A dichotomous key is a map of characteristics that looks very much like a family tree. By moving from general to specific characteristics, it can be used to classify a single animal from a large group.
Prepare a list of dogs for identification via the key. You should have the common name for each dog and a picture.
Examine the dogs and list their particular characteristics. Characteristics may include short hair, long hair, under two feet tall, the color of the dog's hair, long or short tail, etc. Write these down under the name of each dog.
Check all of the dogs' characteristics to ensure that no two dogs share the exact same particular characteristics.
Select the most common type of characteristic. It may be, for instance, whether the dog has long or short hair. On a blank sheet of paper, write long hair on one side and short hair on the other.
Look through all of the dogs with long hair (or whichever trait you have chosen) and look for the next most common characteristic. For example, this could be height. Under the the words "long hair" you would write "over two feet tall" and "under two feet tall", connected to "long hair" with a line. The format should resemble a family tree. Do the same with the short-haired dogs.
Continue this process until all of the characteristics for each dog have been drawn out. Once you reach a dead end, for instance, if you only had one dog with long hair and and a height of over two feet, write the dogs name, i.e. "Golden Retriever".
Test your key with a friend by having them identify all of the dogs using the dichotomous key alone. If they are able to do this, you have made a successful dichotomous key for dogs.
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