In biology, a strain is a low-level taxonomic rank used at the intraspecific level (within a species). Strains are often seen as inherently artificial concepts, characterized by a specific intent for genetic isolation. This is most easily observed in microbiology where strains are derived from a single cell colony and are typically quarantined by the physical constraints of a Petri dish. Strains are also commonly referred to within virology, botany, and with rodents used in experimental studies.
A strain is a genetic variant or subtype of a microorganism (e.g., virus or bacterium or fungus). For example, a "flu strain" is a certain biological form of the influenza or "flu" virus. These flu strains are characterized by their differing isoforms of surface proteins. New viral strains can be created due to mutation or swapping of genetic components when two or more viruses infect the same cell in nature. These phenomena are known respectively as antigenic drift and antigenic shift. Microbial strains can also be differentiated by their genetic makeup using metagenomic methods to maximize resolution within species. This has become a valuable tool to analyze the microbiome.
Scientists have engineered flu virus strains pandemic in humans in order to study their behavior. Funding for this research has been controversial as a result of safety concerns, and has been halted at times. However, this research continues today.
In biotechnology, microbial strains have been engineered to establish metabolic pathways suitable for treating a variety of applications. Historically, a major effort of metabolic research has been devoted to the field of biofuel production. Optimized strains of E. coli are typically are used for this application. E. coli are also often used as a chassis for the expression of simple proteins. These strains, such as BL21, are engineered to minimize protease activity, hence enabling potential for high efficiency industrial scale protein expression. In the case of complex proteins including biologics, mammalian strains are typically used for expression. See Chinese hamster ovary cell.
Yeasts are the most common subjects of eukaryotic strain engineering, especially with respect to industrial fermentation.
E. coli is most common species for prokaryotic strain engineering. Scientists have succeeded in establishing viable minimal genomes from which new strains can be developed. These minimal strains provide a near guarantee that experiments on genes outside the minimal framework will not be effected by non-essential pathways.
The term has no official ranking status in botany; the term refers to the collective descendants produced from a common ancestor that share a uniform morphological or physiological character. A strain is a designated group of offspring that are either descended from a modified plant (produced by conventional breeding or by biotechnological means), or which result from genetic mutation.
As an example, some rice strains are made by inserting new genetic material into a rice plant, all the descendants of the genetically modified rice plant are a strain with unique genetic information that is passed on to later generations; the strain designation, which is normally a number or a formal name, covers all the plants that descend from the originally modified plant. The rice plants in the strain can be bred to other rice strains or cultivars, and if desirable plants are produced, these are further bred to stabilize the desirable traits; the stabilized plants that can be propagated and "come true" (remain identical to the parent plant) are given a cultivar name and released into production to be used by farmers.
A laboratory mouse or rat strain is a group of animals that is genetically uniform. Strains are used in laboratory experiments. Mouse strains can be inbred, mutated, or genetically engineered, while rat strains are usually inbred. A given inbred rodent population is considered genetically identical after 20 generations of sibling-mating. Many rodent strains have been developed for a variety of disease models, and they are also often used to test drug toxicity.
The common fruit fly (Drosophila melanogaster) was among the first organisms used for genetic analysis, has a simple genome, and is very well understood. It has remained a popular model organism for many other reasons, like the ease of its breeding and maintenance, and the speed and volume of its reproduction. Various specific strains have been developed, including a flightless version with stunted wings (also used in the pet trade as live food for small reptiles and amphibians).
A breed is a specific group of domestic animals having homogeneous appearance (phenotype), homogeneous behavior, and/or other characteristics that distinguish it from other organisms of the same species. Breeds are formed through genetic isolation and either natural adaptation to the environment or selective breeding, or a combination of the two. Despite the centrality of the idea of "breeds" to animal husbandry and agriculture, no single, scientifically accepted definition of the term exists. A breed is therefore not an objective or biologically verifiable classification but is instead a term of art amongst groups of breeders who share a consensus around what qualities make some members of a given species members of a nameable subset.When bred together, individuals of the same breed pass on these predictable traits to their offspring, and this ability – known as "breeding true" – is a requirement for a breed. Plant breeds are more commonly known as cultivars. The offspring produced as a result of breeding animals of one breed with other animals of another breed are known as crossbreeds or mixed breeds. Crosses between animal or plant variants above the level of breed/cultivar (i.e. between species, subspecies, botanical variety, even different genera) are referred to as hybrids.Index of evolutionary biology articles
This is a list of topics in evolutionary biology.Mathematical modelling of infectious disease
Mathematical models can project how infectious diseases progress to show the likely outcome of an epidemic and help inform public health interventions. Models use some basic assumptions and mathematics to find parameters for various infectious diseases and use those parameters to calculate the effects of different interventions, like mass vaccination programmes. The modelling can help in deciding which intervention/s to avoid and which to trial.Subspecies
In biological classification, the term subspecies refers to a unity of populations of a species living in a subdivision of the species' global range and varies from other populations of the same species by morphological characteristics.
A subspecies cannot be recognized independently. A species is either recognized as having no subspecies at all or at least two, including any that are extinct. The term is abbreviated subsp. in botany and bacteriology, or ssp. in zoology. The plural is the same as the singular: subspecies.
In zoology, under the International Code of Zoological Nomenclature, the subspecies is the only taxonomic rank below that of species that can receive a name. In botany and mycology, under the International Code of Nomenclature for algae, fungi, and plants, other infraspecific ranks, such as variety, may be named. In bacteriology and virology, under standard bacterial nomenclature and virus nomenclature, there are recommendations but not strict requirements for recognizing other important infraspecific ranks.
A taxonomist decides whether to recognize a subspecies or not. A common criterion for a subspecies is its ability of interbreeding with a different subspecies of the same species and producing fertile offspring. In the wild, subspecies do not interbreed due to their geographic isolation and sexual selection. The differences between subspecies are usually less distinct than the differences between species.