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Shahbaz Aslam. Topic. Biological Keys. Contents. What is biological Key? Types of keys. Dichotomous Keys Polytomous Keys Example of Classification of Elephant Common problems in key usage. What is A Biological Key? .

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ShahbazAslam


Topic

Topic

Biological Keys


Contents
Contents

  • What is biological Key?

  • Types of keys.

  • Dichotomous Keys

  • Polytomous Keys

  • Example of Classification of Elephant

  • Common problems in key usage


What is a biological key
What is A Biological Key?

  • A biological key is a list or a series of questions that asks questions about physical characteristics.

  • A biological key is used to determine the classification of any living object. Classifications include kingdom, phylum, class, order & so on.


Types of keys
Types of keys.

  • There are 2 major types of Biological keys

  • Dichotomous Keys

  • Polytomous Keys


Dichotomous keys
Dichotomous Keys

  • Dichotomous means divided in 2 parts.

  • Such keys in which each following step or question has only 2 choices or answers are called Dichotomous Keys. These are most common biological keys.

  • For example, an organism may be:

  • Microscopic or Macroscopic.

  • If it is microscopic then it may be:

  • Prokaryote or eukaryote.


Organism

Microscopic Macroscopic

ProkaryoticEukaryotic Autotrophic Hetrotrophic

(Kingdom Monera)(Kingdom Protista)

Decomposers Consumers

( Kingdom Fungi) ( Kingdom Animalia)


Dichotomous keys given by aristotle
Dichotomous Keys Given By Aristotle

  • Aristotle was one of the great thinkers of his time. One of his achievements was to outline a scientific classification of animals.   He observed many animals to find features by which to classify them.  


Polytomous keys
Polytomous Keys

  • Such keys in which each following step or question has more than 2 choices or answers are called Polytomous Keys.


Example of classification of elephant
Example of Classification of Elephant

  • Key1: What is the size of elephant?

  • Since we don't need to magnify an elephant in order to see it, the elephant is macroscopic.

  • Key2: We are asked whether or not the elephant is autotrophic or heterotrophic?

  • Clearly, the elephant is heterotrophic; it eats plants in order to live.




  • Key 5: Whether the animal has a jaw or beak? consumer.?

  • It has a jaw.

  • Key 6: If there are scales on the skin?

  • There are no scales.

  • Key 7: This key asks about hair or feathers?

  • The picture shows hair on the head.

  • Thus, we learn that the elephant is in

  • Class Mammalia





Common problems in key usage
Common problems in key usage this key.

  • Key users must overcome many practical problems, such as:

  • Variant forms: The key may identify only some forms of the species, such as adult males (or, more rarely, females). Keys for larvae identification may consider only the final instar. (This is not the case, however, of keys used in forensic identification of fly larvae.)

  • Incomplete coverage: Species and groups that are difficult to identify or that have been poorly characterized may have been left out of the key, or may be mentioned only in introductory text.


Cont…. this key.

  • Lighting and magnification: Very few keys give details of how the specimen was viewed (the magnification, lighting system, angle of view etc.). This can cause problems. The author may, for instance refer to tiny bristles, hairs or chaetae--but how tiny?

  • Language: Very few keys are multilingual. Translations of a key may be incorrect or misleading. Many keys contain vague words that do not translate.

  • Obsolescence: Older keys may not include more recently described species. They may also use outdated species names, which must then be mapped to the current ones