How to Make a Dichotomous Key: 10 Steps (with Pictures) - wikiHow (2022)

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1Analyzing Your Specimens

2Creating Your Key

3Completing Your Dichotomous Key

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Co-authored byBess Ruff, MA

Last Updated: March 9, 2022

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A dichotomous key is a way of identifying specimens based on contrasting statements, usually about physical characteristics. By drawing a series of contrasts, you are able to narrow down the specimen until you can correctly identify it. Dichotomous keys are often used in the sciences, such as biology and geology. To make your own dichotomous key, first, select the characteristics you can use to contrast your specimens, then formulate these as a series of statements or questions you can use to narrow them down.

Things You Should Know

  • Create a list of characteristics for the specimens you're trying to identify. For example, you might list traits like black fur, striped fur, spotted fur, long tail, short tail, and so on.
  • Focus primarily on characteristics that can be used to differentiate the specimens. If one specimen has fur and another has feathers, those would be good characteristics to list.
  • Use the listed characteristics to divide your specimens into groups, like specimens with feathers and specimens with scales.
  • Start with two groups, then divide each of those into two groups, and so on until each specimen is differentiated from all of the other specimens.
  1. 1

    List the characteristics of your specimens. Start by considering the specimens you are trying to identify and insert into a dichotomous key. Note characteristics that define the things you are looking at, and start listing them out.

    • If you are trying to create a dichotomous key for a series of animals, you might see that some have feathers, some swim, some walk on legs, etc.
    • For example, if you are trying to differentiate a set of big cats, you might note that some are brown, some are black, some have stripes, some have spots, some have long tails, some have short tails, and so on.
  2. 2

    Look for principles of exclusion. A dichotomous key works by the process of elimination, so you want to note characteristics that can be used to differentiate the things you are examining. For example, if some of the specimens you are looking at have feathers but others have fur, then "feathers" is a good distinguishing characteristics.

    • However, a trait all of the animals share is not a good distinguishing factor. For example, since all big cats are warm-blooded, you wouldn't want to use that trait on your dichotomous key.

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  3. 3

    Determine the most general characteristics. You want to create a dichotomous key based on increasingly specific differentiations, so you’ll have to order the characteristics of your specimens from general to specific. This will help divide your specimens ever-smaller groups. For instance:

    • When making your dichotomous key for big cats, you may find that some of the cats you are analyzing have dark fur, and some have light fur. You may also see that all of them have short hair. Finally, you see that some of them have long tails, but some of them have no tails at all.
    • You would start your key with a question/statement about fur color. You wouldn’t need to ask a question about fur length, since all of the examples have short fur. You would follow up with a question about tail length, since tails are not common to all of the cats, and therefore are a less general characteristic.
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  1. 1

    Formulate a series of differentiating steps. It’s up to you whether you want to use questions or statements, though you may find questions more intuitive. In either case, each question or statement should only break the specimens you are looking at into two groups.

    • For example, "The cat has solid-colored fur" or "The cat has patterned fur" are statements that can be used to break specimens down into two groups.
    • Include the question "Does the cat have solid-colored fur?" in your dichotomous key to divide the animals. If the answer is "Yes," then the cat belongs in the solid-colored fur group. If the answer is "No," then the cat belongs in the patterned-fur group.
  2. 2

    Divide your specimens into two groups. This will be the first differentiation. It should be based on the most general aspect of your specimens, so review the list of physical characteristics you developed. You can refer to the first two groups as A and B.

    • For example, separate your cats based on whether they have solid or patterned fur.
    • Similarly, if you note that all of your specimens have either feathers or scales, then these could be your groups A and B. You can begin your key with the question "Does the animal have feathers?"
  3. 3

    Subdivide each of the first two groups into two more groups. Group A and group B will each be broken down into more specific groups (C and D), based on the next differentiating characteristic.

    • For instance, you might notice that some of the animals in group A swim, and others don’t. This differentiation can form level C/D for group A.
    • Likewise, you might see that some of the animals in group B have legs, and others don’t. This differentiation can form level C/D for group B.
  4. (Video) Making a dichotomous key

    4

    Continue subdividing your groups. Keep formulating more questions or statements of ever-increasing specificity based on the physical characteristics you identified. Come up with characteristics that can break your specimens down as needed into groups E/F, G/H, etc. Eventually, you will reach the point until you have questions that only ask you to differentiate two specimens, and your key will be complete.

    • Some specimens will be differentiated before the end, as you work through your contrasting characteristics. For instance, you might find yourself looking at some birds, and some reptiles. You will break them down into these groups, then sub-divide the birds.
    • Two of the birds swim, but one of them does not. The single land bird will be identified as such, but you will have to further differentiate the swimming birds.
    • In this case, you notice that one of the swimming birds is ocean-going, and one is not. This characteristic can allow you to identify them more precisely (e.g., as a gull and a duck).
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  1. 1

    Draw it out as a chart, if you want. A dichotomous key can be text-based, simply a series of questions. However, it can help to visualize the material in some way. For instance, you can create a "tree diagram" where each successive level of differentiation forms another branch of the tree.

    • You could also try organizing your key in the style of a flow chart. For instance, have a box that asks a question like "Does the cat have dark fur?" Then, have a "Yes" arrow leading one way, and a "No" arrow leading another way. The ends of the arrows can lead to new boxes where you ask the next questions.
  2. 2

    Test out your dichotomous key. Once you have all of your information down and organized in your key, run through the key with a specimen in mind to see if it works. For example, say you have a dichotomous key that helps identify various animals. Take a specimen and work through the key’s questions until it leads you to an identification through the process of elimination:

    • Q: "Does the animal have feathers?" A: "No" (it has scales, so it is a reptile).
    • Q: "Does the reptile have legs?" A: "No" (it is a snake, either a cobra or a python, given your specimens).
    • Q: "Does the snake have a hood?" A: "No" (so it is not a cobra).
    • Your specimen is identified as a python.
  3. 3

    Troubleshoot, if necessary. You might find that your key isn’t working correctly, and need to adjust it. For instance, you may not have ordered your questions in an increasingly more specific way, and might need to reorganize them. Likewise, your key might not break your specimens down in the most logical way, so try reframing your questions.

    • For instance, "Does the cat have solid-colored fur or stripes?" is not a useful question for a dichotomous key. This question might differentiate solid-colored and striped cats from cats with spotted fur. However, since solid-colored and striped fur are themselves very different, this is not a useful category to work with.
    • Instead, you might first have a question that asks about solid-colored vs. patterned fur, then follow up with another level of questions like "Does the cat have black fur?" and "Does the cat have stripes?"
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  • Question

    How can I make a dichotomous key on plants?

    How to Make a Dichotomous Key: 10 Steps (with Pictures) - wikiHow (13)

    Community Answer

    (Video) How to make a Dichotomous Key

    Just as the article said, make notes on properties of the plants. Pay close attention to details that can help distinguish one individual plant from the rest of the plants. Some of these differentiation details can be shape and texture of the leaf, position of the leaf, leaf color, etc.

  • Question

    If I have three characteristics such as asymmetry, radial symmetry and bilateral symmetry, how do I create a dichotomous key?

    How to Make a Dichotomous Key: 10 Steps (with Pictures) - wikiHow (14)

    Community Answer

    If you have more than two choices, find a logical way to group some together. In this case, you can first ask whether they are asymmetrical or symmetrical.

  • Question

    How can I construct a butterfly, a mosquito, a cockroach, and a housefly in the dichotomous?

    How to Make a Dichotomous Key: 10 Steps (with Pictures) - wikiHow (15)

    Community Answer

    It can go like this, you can add different species of housefly or cockroach or mosquito or whatever you like. 1: Does the insect have long antennae? Yes (Go to 2). No (Go to 3). 2: Does the insect have a long thorax? Yes (Go to 4). No (Go to 3). 3: Does the insect have four wings? Yes (Butterfly). No (Go to 5) 4: Does the insect have a long proboscis/tongue? Yes (Mosquito). No (Go to 5). 5: Does the insect have two spikes at the bottom of it's thorax? Yes (Cockroach). No (Housefly).

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      About This Article

      Article SummaryX

      To make a dichotomous key, start by making 2 groups, for example big cats with spots versus big cats without spots. Then, subdivide each of these groups into 2 more groups, like big cats with short tails, big cats with long tails, and big cats with no tails. Continue subdividing your groups until you can’t break them down anymore. Once your key is complete, draw it out as a “tree diagram,” in which each subdivided category forms another branch of the tree. Or, organize your findings into a flow chart. To learn how to test out your dichotomous key, keep reading!

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      FAQs

      How many steps are in a dichotomous key? ›

      Dichotomous literally means dividing into two parts (Merriam-Webster, 2014). A dichotomous key provides users with a series of statements with two choices that will eventually lead to the correct identification of the organism.

      How do you fill out a dichotomous key? ›

      And you want to find out what it is keys help you to identify your species. Here's an example of how

      What is a dichotomous key * Your answer? ›

      A dichotomous key is an identification chart that helps users identify organisms, objects or anything else by choosing between questions/statements presented in the chart until they reach a conclusion.

      What is a dichotomous key example? ›

      Example Dichotomous Key

      Example objects to identify: apple tree, water-lily, fir tree, dandelion, astroturf, seaweed. Dichotomous keys may be simple or complex depending on what is being identified.

      What is a good example of a dichotomous key question? ›

      For example, in tree identification, a dichotomous key might ask whether the tree has leaves or needles. The key then directs the user down one list of questions if the tree has leaves, and a different question list if it has needles.

      How do you make a key? ›

      How to Make Dichotomous Keys - YouTube

      What are 2 ways of creating a dichotomous key? ›

      Dichotomous keys are usually represented in one of two ways: As a branching flowchart (diagrammatic representation) As a series of paired statements laid out in a numbered sequence (descriptive representation)

      How many questions are there in a dichotomous key? ›

      A dichotomous key is a process of identifying an organism with a series of steps, each containing two questions. The answers lead you along a path until the organism is identified.

      What are the 3 types of dichotomous keys? ›

      The three common types of dichotomous keys are the nested, linked, and branched dichotomous keys. In the nested type, we get the answer of each statement nested right next to it. In the linked types, we use lists of text to identify objects. We use a tree diagram to make the dichotomous key in the branched type.

      What is dichotomous key PDF? ›

      Dichotomous Keys. Classification is the science of dividing organisms into groups and sub-groups based on. how they are related. A tool called a dichotomous key is an organized list of characteristics. that can be used to identify organisms.

      What are the rules of a dichotomous key? ›

      Rules for Using Dichotomous Keys:
      • Read both choices in a couplet carefully. ...
      • Keep notes telling what sequence of identification steps you took. ...
      • If you are unsure of which choice to make in a couplet, follow both forks (one at a time). ...
      • Work with more than one sample if at all possible.
      26 May 2019

      What step do you always start with when using a dichotomous key? ›

      How to use a Dichotomous Key - YouTube

      What are the 7 levels of classification? ›

      His major groupings in the hierarchy of groups were, the kingdom, phylum, class, order, family, genus, and species; seven levels of groups within groups. This was arbitrary, and more levels have been added over the years since the time of Linnaeus.

      What is dichotomous key for kids? ›

      A dichotomous key is a tool that can be used to identify organisms or objects in the natural world, such as plants, animals, or rocks. The key consists of a series of paired statements or clues about features or characteristics, providing a stepwise guide toward identifying each entity.

      Why do we use dichotomous keys? ›

      Dichotomous keys are most commonly used to identify plant and animal species based on their characteristics. Dichotomous key is very useful for identifying an organism as a member of a single, closely related group of organisms. In many environments, this is sufficient for complete identification of the species.

      Why are dichotomous keys used Brainly? ›

      Answer: A dichotomous key is a tool that allows the user to determine the identity of items in the natural world, such as trees, wildflowers, mammals, reptiles, rocks, and fish. Keys consist of a series of choices that lead the user to the correct name of a given item.

      How do you make a dichotomous question? ›

      Belonging to the closed-ended family of questions, dichotomous questions are ones that only offer two possible answers, which are typically presented to survey takers in the following format – Yes or No, True or False, Agree or Disagree and Fair or Unfair.

      What is dichotomous type of questions explain with examples? ›

      The dichotomous question is a question that can have two possible answers. Dichotomous questions are usually used in a survey that asks for a Yes/No, True/False, Fair/Unfair or Agree/Disagree answers. They are used for a clear distinction of qualities, experiences, or respondent's opinions.

      How do you say dichotomous key? ›

      Dichotomous key Meaning - YouTube

      What is a key draw? ›

      Definition of key drawing

      : an outline drawing that indicates position of printed matter or that serves as a guide for color separation.

      How do you draw a key ring? ›

      How to draw a Keyring Real Easy - YouTube

      What is key in biology? ›

      Keys are used to identify different species. A key will usually ask questions based on easily identifiable features of an organism. Dichotomous keys use questions to which there are only two answers. They can be presented as a table of questions, or as a branching tree of questions.

      How do you make a dichotomous key for birds? ›

      Dichotomous Key - YouTube

      What is a dichotomous key quizlet? ›

      A dichotomous key is a tool that allows the user to determine the identity of items in the natural world, such as trees, wildflowers, mammals, reptiles, rocks, and fish. Keys consist of a series of choices that lead the user to the correct name of a given item. "Dichotomous" means "divided into two parts".

      How do you make a bracketed dichotomous key? ›

      How to Make a Dichotomous Key - YouTube

      How are statements organized in dichotomous keys? ›

      A dichotomous key uses a series of statements, descriptions, or yes or no questions grouped into pairs, which eventually lead to the correct identity of a specimen or organism. An example of a dichotomous key designed to be used by children to classify common invertebrates they may find in a garden is shown below.

      What is a dichotomous key for insects? ›

      Summary of the Insect Dichotomous Key:

      A dichotomous key is a series of statements or characteristics that can be used to identify an organism. When you use a dichotomous key, you examine an animal's boarder, more general characteristics first and then look at the more specific characteristics at the end.

      Which question is most likely to be found in a dichotomous key for identifying a tree by its leaves? ›

      Which question is most likely to be found in a dichotomous key for identifying a tree by its leaves? What is the shape of the tree's leaves?

      How do I make a dichotomous key for my dog? ›

      1. 1 Prepare a list. Prepare a list of dogs for identification via the key. ...
      2. 2 Examine the dogs. Examine the dogs and list their particular characteristics. ...
      3. 3 Check all. ...
      4. 4 Select the most common type. ...
      5. 5 Look. ...
      6. 6 Continue this process. ...
      7. 7 Test your key with a friend.

      What are the 8 levels of classification from most broad to most specific? ›

      The classification system commonly used today is based on the Linnean system and has eight levels of taxa; from the most general to the most specific, these are domain, kingdom, phylum (plural, phyla), class, order, family, genus (plural, genera), and species.

      Which of the following is the best way to develop a dichotomous key? ›

      5 Which of the following is the best way to develop a dichotomous key? Move from observing the most specific traits that can divide the organisms to the most obvious traits, offering 2 choices each time.

      What is a dichotomous key PPT? ›

      A dichotomous key is a tool that allows the user to determine the identity of items in the natural world based on the items characteristics.

      What does Di mean in dichotomous? ›

      The prefix “di-” means two. A dichotomous key breaks down identification into two mutually exclusive options at each step.

      What does the term dichotomous mean? ›

      Definition of dichotomous

      1 : dividing into two parts. 2 : relating to, involving, or proceeding from dichotomy the plant's dichotomous branching a dichotomous approach can't be split into dichotomous categories.

      What is a dichotomous key for leaves? ›

      Regrading the compound leaves, serrated and entire leaves. A dichotomous key is a useful scientific tool for identifying various organisms based on their observable characteristics. Dichotomous keys are made up of a series of statements, each with two options, that guide users to the proper identification.

      What features could a person use to build a dichotomous key for plants? ›

      To make a dichotomous key you will choose physical characteristics that can be used to divide a collection into two parts. Possible physical characteristics to use include plant size, plant shape, leaf shape, stem type, color, and presence of seeds, fruits or flowers.

      What is an identification key in science? ›

      An identification key, also known as a taxonomic key, is a useful tool for identifying unknown organisms. Keys are constructed so that the user is presented with relevant information in a structured form.

      What are 2 ways of creating a dichotomous key? ›

      Dichotomous keys are usually represented in one of two ways: As a branching flowchart (diagrammatic representation) As a series of paired statements laid out in a numbered sequence (descriptive representation)

      How many questions are there in a dichotomous key? ›

      A dichotomous key is a process of identifying an organism with a series of steps, each containing two questions. The answers lead you along a path until the organism is identified.

      When constructing a key it is best to start with? ›

      When constructing a key, it is best to start with characteristics and proceed to characteristics.

      What are the 3 types of dichotomous keys? ›

      The three common types of dichotomous keys are the nested, linked, and branched dichotomous keys. In the nested type, we get the answer of each statement nested right next to it. In the linked types, we use lists of text to identify objects. We use a tree diagram to make the dichotomous key in the branched type.

      What is dichotomous key PDF? ›

      Dichotomous Keys. Classification is the science of dividing organisms into groups and sub-groups based on. how they are related. A tool called a dichotomous key is an organized list of characteristics. that can be used to identify organisms.

      What step do you always start with when using a dichotomous key? ›

      How to use a Dichotomous Key - YouTube

      What are the 7 levels of classification? ›

      His major groupings in the hierarchy of groups were, the kingdom, phylum, class, order, family, genus, and species; seven levels of groups within groups. This was arbitrary, and more levels have been added over the years since the time of Linnaeus.

      Why are dichotomous keys used Brainly? ›

      Answer: A dichotomous key is a tool that allows the user to determine the identity of items in the natural world, such as trees, wildflowers, mammals, reptiles, rocks, and fish. Keys consist of a series of choices that lead the user to the correct name of a given item.

      What is dichotomous key for kids? ›

      A dichotomous key is a tool that can be used to identify organisms or objects in the natural world, such as plants, animals, or rocks. The key consists of a series of paired statements or clues about features or characteristics, providing a stepwise guide toward identifying each entity.

      Why is dichotomous key called that? ›

      “Dichotomous” means “divided into two parts.” That is why dichotomous keys always give two choices in each step. In each step, the user is presented with two statements based on characteristics of the organism.

      How do you say dichotomous key? ›

      Dichotomous key Meaning - YouTube

      Why do you need to use dichotomous keys that are specific for your area? ›

      Dichotomous keys are very useful because they allow non-expert users to identify organisms, directing them to study known important organisms.

      What features could a person use to build a dichotomous key for plants? ›

      To make a dichotomous key you will choose physical characteristics that can be used to divide a collection into two parts. Possible physical characteristics to use include plant size, plant shape, leaf shape, stem type, color, and presence of seeds, fruits or flowers.

      Which question is most likely to be found in a dichotomous key for identifying a tree by its leaves? ›

      Which question is most likely to be found in a dichotomous key for identifying a tree by its leaves? What is the shape of the tree's leaves?

      What is a dichotomous key for leaves? ›

      Regrading the compound leaves, serrated and entire leaves. A dichotomous key is a useful scientific tool for identifying various organisms based on their observable characteristics. Dichotomous keys are made up of a series of statements, each with two options, that guide users to the proper identification.

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