Dichotomus key - cretittiotou

Dichotomous Key

Word origin: Latin dichotomos, Greek dichótomos. 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. For instance, you may not have ordered your questions in an increasingly more specific way, and might need to reorganize them.

Multiple diagnostic keys may be offered for the same group of organisms: Diagnostic keys may be designed for field or laboratory use, for summer or winter use, and they may use geographic distribution or preference of organisms as accessory characteristics. Lobes or teeth rounded or blunt-pointed, no bristles: 7 6. To test it, you can identify each person in the group by going through the key and seeing if the right name comes up.

Dichotomous Key - You may also see that all of them have short hair.

In , a single-access key also called dichotomous key, sequential key, analytical key, or pathway key is an where the sequence and structure of identification steps is fixed by the author of the key. At each point in the decision process, multiple alternatives are offered, each leading to a result or a further choice. Single access keys are closely related to or. However, to improve the usability and reliability of keys, many single-access keys incorporate , changing the tree structure into a. Single-access keys have been in use for several hundred years. They may be printed in various styles e. In the latter case, either a longer part of the key may be displayed optionally hyperlinked , or only a single question may be displayed at a time. If the key has several choices it is described as polychotomous or polytomous. If the entire key consists of exactly two choices at each branching point, the key is called dichotomous. The majority of single-access keys are dichotomous. Any single-access key organizes a large set of items into a structure that breaks them down into smaller, more accessible subsets, with many keys leading to the smallest available classification unit a or typically in the form of. However, a trade-off exists between keys that concentrate on making identification most convenient and reliable diagnostic keys , and keys which aim to reflect the of organisms synoptic keys. The first type of keys limits the choice of characteristics to those most reliable, convenient, and available under certain conditions. Multiple diagnostic keys may be offered for the same group of organisms: Diagnostic keys may be designed for field or laboratory use, for summer or winter use, and they may use geographic distribution or preference of organisms as accessory characteristics. They do so at the expense of creating artificial groups in the key. An example of a diagnostic key is shown below. It is not based on the classification of the included species — compare with the. In contrast, synoptic keys follow the classification as close as possible. Where the classification is already based on phylogenetic studies, the key represents the evolutionary relationships within the group. To achieve this, these keys often have to use more difficult characteristics, which may not always be available in the field, and which may require instruments like a hand lens or microscope. Because of , superficially similar species may be separated early in the key, with superficially different, but genetically closely related species being separated much later in the key. An example of a synoptic key corresponding to the diagnostic key shown below is shown further below. In , and characteristics often are important for primary taxonomic classification: Example of a diagnostic dichotomous key for some eastern based on characteristics 1. Leaves usually without teeth or lobes: 2 1. Leaves usually with teeth or lobes: 5 2. Leaves evergreen: 3 2. Leaves not evergreen: 4 3. Mature plant a large tree — Quercus virginiana 3. Mature plant a small shrub — Quercus minima 4. Leaf narrow, about 4-6 times as long as broad — Quercus phellos 4. Leaf broad, about 2-3 times as long as broad — Quercus imbricaria 5. Lobes or teeth bristle-tipped: 6 5. Lobes or teeth rounded or blunt-pointed, no bristles: 7 6. Leaves mostly with 3 lobes — Quercus marilandica 6. Leaves mostly with 7-9 lobes — Quercus rubra 7. Leaves with 5-9 deep lobes — Quercus alba 7. Leaves with 21-27 shallow lobes — Quercus prinus This key first differentiates between oaks with entire leaves with normally smooth margins , , , and other oaks with lobed or toothed leaves. The following steps created smaller and smaller groups e. Example of a synoptic taxonomic dichotomous key for some eastern , reflecting taxonomic classification 1. Styles short; mature in 6 months, sweet or slightly bitter, inside of acorn shell hairless Quercus sect. Quercus, : 2 1. Styles long, acorns mature in 18 months, very bitter, inside of acorn shell woolly Quercus sect. Lobatae, : 5 2. Leaves evergreen: 3 2. Leaves not evergreen: 4 3. Mature plant a large tree — Quercus virginiana 3. Mature plant a small shrub — Quercus minima 4. Leaves with 5-9 deep lobes — Quercus alba 4. Leaves with 21-27 shallow lobes — Quercus prinus 5. Leaves usually without teeth or lobes: 6 5. Leaves usually with teeth or lobes: 7 6. Leaf narrow, about 4-6 times as long as broad — Quercus phellos 6. Leaf broad, about 2-3 times as long as broad — Quercus imbricaria 7. Leaves mostly with 3 lobes — Quercus marilandica 7. Leaves mostly with 7-9 lobes — Quercus rubra The distinction between dichotomous bifurcating and polytomous multifurcating keys is a structural one, and identification key software may or may not support polytomous keys. This distinction is less arbitrary than it may appear. Allowing a variable number of choices is disadvantageous in the nested display style, where for each couplet in a polytomous key the entire key must be scanned to the end to determine whether more than a second lead may exist or not. However, the latter consideration can easily be accommodated in a polytomous key where couplets based on a single characteristic may have more than two choices, and complex statements may be limited to two alternative leads. Another structural distinction is whether only lead statements or question-answer pairs are supported. The second style is well known from testing and therefore more intuitive for beginners. Lead style Single-access keys may be presented in different styles. With a large key this can lead to much whitespace in print, and consequently little remaining room for lead text and illustrations. At the end of each lead some form of pointer a numbering system, hyperlinks, etc. The nested style gives an excellent overview over the structure of the key. With a short key and moderate indentation it can be easy to follow and even backtrace an erroneous identification path. The nested style is problematic with polytomous keys, where each key must be scanned to the end to verify that no further leads exist within a couplet. It also does not easily support reticulation which requires a link method similar to the one used in the linked style. A large amount of knowledge about reliable and efficient identification procedures may be incorporated in good single-access keys. Characteristics that are reliable and convenient to observe most of the time and for most species or taxa , and which further provide a well-balanced key the leads splitting number of species evenly will be preferred at the start of the key. However, in practice it is difficult to achieve this goal for all taxa in all conditions. If the information for a given identification step is not available, several potential leads must be followed and identification becomes increasingly difficult, Although software exists that helps in skipping questions in a single-access key, the more general solution to this problem is the construction and use of , allowing a free choice of identification steps and are easily adaptable to different taxa e.

Dichotomous keys are very useful for identifying an as a member of a single, closely-related group of organisms. Develop a dichotomous key to identify the snacks. Lobatae, : 5 2. Group A and group B will each be broken down into more specific groups C and Dbased on the dichotomus key differentiating characteristic. DNA analysis and share information internationally it is important to have systems in place to identify and dichotomus key organisms. Bean has dark pigments Go to 3 3a. You might also like: Today's featured page: grade-level estimate for this page: 5th - 6th Make a Dichotomous Key: Classroom Activity A dichotomous key is a series of questions which leads to the identification of an item. Bean is reddish-brown Kidney bean B. At each point in the decision process, multiple alternatives are offered, each leading to a result or a further choice.