[Biology] Systematics

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INTRODUCTION

  • Systematics is the branch of biology that deals with the classification systems and nomenclature of living organisms.
  • This is the study of distinctive characters of species and their relations to the other species through time.
  • Systematics is the basis of understanding evolution process of life
  • The main objective of this study is to assign scientific names to the organisms, to describe them so that they can be easily identified.
  • Moreover, it also provides an insight of the evolutionary histories and environmental adaptations of organisms.
  • It is also referred to as the study of biodiversity

FIELDS OF SYSTEMATICS

The study of systematics is comprised of three distinctive fields which aid in the classification of organisms:

  • Identification
  • Classification
  • Nomenclature

IDENTIFICATION

  • Identification is used to recognize the correct place of an organism in a system of classification.
  • Identification of an organism is carried out by determining its similarity with an already known organism.
  • It is done with the aid of keys. An identification key, also termed as a taxonomic key, is a useful means of identifying unknown organisms. Keys are established so that the user is presented with relevant information in a structured form.
  • Keys are used for identification and are based on the alternate characters. An organism can be identified easily by selecting and removing the characters present in the key.

CLASSIFICATION

  • Classification is the system of arranging organisms into relevant groups.
  • There are millions of organisms including plants, animals and microorganisms. Each organism is different in one way or the other.
  • It is difficult to remember the names, characters and uses of millions of species.
  • Classification system helps the scientists to organize these organisms so that they can be studied easily.
  • Classification in Systematics can be divided into two closely related and interconnected levels of classification:
  • Taxonomic classification (known as the Linnaean System)
  • Phylogenetic classification

TAXONOMIC CLASSIFICATIONS

  • This type of classification groups living things together based on shared traits i.e. what they look like or what their bodies do.
  • For example, animals that lay eggs and have scales are called reptiles, and animals that have live births and have fur or hair are called mammals.
  • More specifically, all humans share the same characteristics and belong to a group (taxon) of the genus Homo, and species sapien.

PHYLOGENETIC CLASSIFICATIONS

  • This type of classification uses the taxonomic names and further groups organisms on the basis of their evolutionary relationships
  • By looking at each organism’s genes, we know that gorillas (taxonomic term), are more closely related to humans than they are to cockroaches.
  • It can be more easily understood by using daily life as an example.
  • If you were to introduce someone to a group of people, you might start with his/her names (taxonomic classification), and then describe whose sister, brother, uncle, friend the person is or a total stranger (phylogeny).

NOMENCLATURE

  • Nomenclature is the system of naming organisms for easy identification.
  • Using the scientific name, an organism can easily be identified as well as information about its taxon can be derived from the name as well

TYPES OF NOMENCLATURE

  • Binomial nomenclature
  • Polynomials nomenclature
  • Trinomial nomenclature

BINOMIAL NOMENCLATURE

  • Binomial nomenclature is a binomial system of naming an organism.
  • Each organism’s name consists of two parts , the first name is genus and it starts with capital letter.
  • The second part’s name is species and it starts with the small letter.
  • This system was developed by Carolus Linnaeus and is used by biologists all over the world.

FOR EXAMPLE

  • Mangifera indica (Mango); here Mangifera is the generic name and indica is the specie name.
  • In terms of zoology, it is called binary nomenclature
  • While in botanical terms, it is called a binomial classification system.

RULES FOR BINOMIAL NOMENCLATURE

There are certain rules for naming and classifying organisms to avoid any confusion and error:

  1. Names should be in Greek or Latin language.
  2. Generic name begins with capital letter (Mangifera) and is placed before species name, while species name begins with a small letter (indica).
  3. The scientific name should be either underlined or italicized.
  4. Name of the author should be written after species name in an abbreviated form. e.g., Homo sapiens Linn.
  5. It indicates that the species is first described by Linnaeus.

POLYNOMIAL NOMENCLATURE

  • Before 1750, a polynomial nomenclature system was used.
  • In this nomenclature, the organism’s name consists of a series of Latin descriptive words.
  • Such names were lengthy and difficult to learn.

FOR EXAMPLE

TRINOMIAL NOMENCLATURE

This system, devised by Lamarck, the organism is given a name consisting of three words i.e. genus, species, subspecies
FOR EXAMPLE

Brassica oleracea capitata (cabbage)

CODES OF BIOLOGICAL NOMENCLATURE

There are five codes of nomenclature which help to evade errors,

duplication and uncertainty in scientific names:

  • International Code of Botanical Nomenclature (ICBN)
  • International Code of Zoological Nomenclature (ICZN),
  • International Code of Bacteriological Nomenclature (IC Вас N),
  • International Code of Viral Nomenclature (ICVN) and
  • International Code of Nomenclature for Cultivated Plants (ICNCP).

TYPES OF SPECIFICATIONS IN NOMENCLATURE

The ICBN recognizes following several types of specifications in nomenclature:

HOLOTYPE

The original specimen from which the description of new species is established is called holotype.

ISOTYPE

It is the duplicate of holotype (analogous to another branch of the same tree).

LECTOTYPE

This is the specimen selected from original material to serve as nomenclature type when there is no holotype

NEOTYPE

It is a specimen later selected as the single holotype when an ingenious holotype has been lost or destroyed or where the first author never cited a specimen

PARATYPE

In biology, a paratype is a specimen that aids in defining what the scientific name of a species and other taxon actually represents, however it is not the holotype.

SYNTYPE

Any of two or more specimens cited by an author when there is no holotype

It can also be summarized in the following way:

DIFFERENCE BETWEEN TAXONOMY AND SYSTEMATICS

REFERENCES

  • Arihant’s handbook of biology. The living world. Page no: 1-6.
  • NCERT biology; textbook for class 11. The living world. Page no: 1-62.
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