topic biological keys contents what is biological key? types of keys. dichotomous keys polytomous...

Shahbaz Aslam

TopicBiological 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?

• 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.

• There are 2 major types of Biological keys1. Dichotomous Keys2. Polytomous 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

Prokaryotic Eukaryotic Autotrophic Hetrotrophic

(Kingdom Monera) (Kingdom Protista)

Decomposers Consumers

( Kingdom Fungi) ( Kingdom Animalia)

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

• 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

• 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 3: we need to determine whether it is a decomposer or a consumer.?

• Since the elephant eats plants, it is a consumer.

• That tells us that our first classification is kingdom Animalia.

• Key 4: We determine whether or not it has a backbone?

• people ride on elephants' backs or elephants carry heavy loads on their backs. So, elephants have backbones.

• So we learn that the elephant is in • Phylum Chordata

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

• Key 8: whether the elephant is a herbivore or carnivore?

• We already know that elephants eat plants, making them herbivores.

• Key 9: we must decide whether or not the elephant has hooves?

• The feet have skin all the way to the bottom, so there are no hooves.

• Key 10: we are asked whether there is an enlarged trunk?

• Yes, there is. Thus, we know that the elephant is in

• order Proboscidea

• This is as detailed a classification as we can make with this key.

• Then, the elephant classification is:

Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Proboscidea

Common problems in key usage

• 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….

• 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