What is the Difference Between Strain and Species

The main difference between strain and species is that strain is a genetic variant; it is a subtype or culture of a biological species. But, species is the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspringtypically by sexual reproduction. Furthermore, several strains can occur per species while species is the basic unit of classification or organisms and a unit of biodiversity. 

In brief, strain and species are two units of classification of a living organism. However, their usage may vary depending on the situation. 

Key Areas Covered 

1. What is a Strain
     – Definition, Characteristics, Usage
2. What is a Species
     – Definition, Characteristics, Usage
3. What are the Similarities Between Strain and Species
     – Outline of Common Features
4. What is the Difference Between Strain and Species
     – Comparison of Key Differences

Key Terms 

Fertile Offspring, Genetic Characteristics, Species, Strain, Taxonomic Group Difference Between Strain and Species - Comparison Summary

What is a Strain 

A strain is a genetic variant, subtype or culture of a biological species. They are more popularly used in microbiology. Furthermore, a strain originates from a single cell colony, and microorganisms, such as viruses, bacteria, and fungi, have several strains within a species. As an example, a “flu strain” is a certain biological form of influenza or “flu” virus characterized by their differing isoforms of surface proteins. Thereby, a strain significantly carries a particular genetic characteristic, which does not occur within the other members of the species.

Difference Between Strain and Species

Figure 1: H1N1 Viral Strain

Besides, genetic variation is the variation of genomes between individuals in the same species due to the genetic mutations, which occur during sexual reproduction. Usually, genetic variation can be caused by mutations of genes, gene flow, random mating, random fertilization, and crossing over between homologous chromosomes. In addition to that, genetic variation is an important mechanism, which forces evolution through natural selection. Also, it is important in maintaining biodiversity among species, as well.

What is a Species 

A species is a closely related group of organisms with similar characteristics and interbreed to produce a fertile offspring. Also, it is the fundamental unit of the classification of organisms. In order to define a particular species, the similarities in the DNA sequences, morphological, and ecological features can be considered. In the historical means, the origination of species by natural selection is described by Charles Darwin in 1859. Sometimes, a particular species may consist of different breeds with great variations. More often, similar species live in similar habitats since they originate from a common ancestor. However, defining a species may become difficult due to variation within the species.

Main Difference - Strain vs Species

Figure 2: The Butterfly Genus Heliconius Contains Many Similar Species.

Furthermore, species is a taxonomic level of organisms, ranking below a genus. Although it consists of similar individuals who can interbreed with each other, a species comprises the biggest possible gene pool. Also, genes can be transferred between species by horizontal gene transfer. Moreover, particular species is scientifically named by a binomial name; the first part of it is the genus to which the organism belongs to and the second part is the specific name. For example, humans have scientifically named as Homo sapiens; ‘Homo’ is the genus to which humans belong, and ‘sapiens’ is the specific name of humans.  

Similarities Between Strain and Species 

  • Generally, strain and species are two groups of living organisms classified depending on different usages. 
  • Also, the organisms within each group show similar genetic, morphological, and behavioral characteristics. 
  • Besides, the organisms within each group can successfully breed in order to produce a fertile offspring. 

Difference Between Strain and Species 


A strain refers to a genetic variant or subtype of a biological species, while species refers to a group of organisms that can reproduce with one another in nature and produce fertile offspring. 


A strain is a subtype of species, while a species is the basic taxonomic group of classification of organisms. 


A strain is an isolate of a given species with a specific genetic characteristic, while organisms in a species have a genetic similarity sufficient for mating, producing a fertile offspring. 


A strain can be characterized by serotyping, enzyme type, functional traits, and protein plasmid characterization, etc., while species can be characterized by genetic, biochemical and phenotypic criteria. 


In brief, a strain is an isolate of a particular species, bearing a specific genetic characteristic in comparison to the other organisms of the same species. Generally, a species refers to a group of organisms with genetic similarity to a certain degree, which is sufficient for producing a fertile offspring by mating. Therefore, a strain is a subtype or a genetic variant of a particular species where the species can have several strains. Hence, the main difference between strain and species is in their genetics.   


1. Dijkshoorn, L. “Strain, Clone, and Species: Comments on Three Basic Concepts of Bacteriology.” J. Med. Microbiol., vol. 49, 2000, pp. 397–401. Available Here.

Image Courtesy:

1. “H1N1 navbox” By Cybercobra at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia   
2. “Heliconius mimicry” By see Source – Repeating Patterns of Mimicry. Meyer A, PLoS Biology, Vol. 4/10/2006, e341 doi:10.1371/journal.pbio.0040341 (CC BY 2.5) via Commons Wikimedia   

About the Author: Lakna

Lakna, a graduate in Molecular Biology and Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things. She has a keen interest in writing articles regarding science.

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