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Dichotomous Keys
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A dichotomous key is a tool that scientists can use to identify an unknown organism or specimen.
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Examples include… insects Dichotomous Keys
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trees Dichotomous Keys
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rocks Dichotomous Keys
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and shells. Dichotomous Keys
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The word dichotomous means “divided in two parts.”
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Characteristics of a Dichotomous Key
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Consists of a series of two part characteristics of a specimen.
statements that describe the characteristics of a specimen. Dichotomous Keys
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The user is presented with two choices.
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As the user makes a choice, they are led to a new branch of the key.
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In the end, the user is led to the name of the specimen.
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Constructing a Dichotomous Key
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Separate the specimens into two groups based on one characteristic.
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Example: A deck of playing cards could be separated into black cards and red cards. Dichotomous Keys
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Continue to separate the groups until each specimen has its own set of characteristics.
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Red cards can be separated into hearts / diamonds, then
Example: Red cards can be separated into hearts / diamonds, then picture / number cards then male / female cards, etc. Dichotomous Keys
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Make the choice a positive one –
for example, something “is” instead of “is not.” Dichotomous Keys
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Dichotomous Keys Example: 2a.Black card is a spade…….4
2b.Black card is a club……….5 4a.Spade is a picture card…6 4b.Spade is a number card…7 6a.Picture card is male……….8 6b.Picture card is female…..9 Dichotomous Keys
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Start both choices in a pair with the same word.
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Example: Dichotomous Keys 2a.Red card is a heart……….4
2b.Red card is a diamond……5 Dichotomous Keys
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Start the next pair with different words.
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Example: Dichotomous Keys 2a.Red card is a heart……….4
2b.Red card is a diamond……5 4a.Heart is picture card…….6 4b.Heart is number card…….7 6a.Picture card is male……….8 6b.Picture card is female……9 Dichotomous Keys
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There should be one less step than the total number of
specimens to be identified. Dichotomous Keys
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