Reassortment is the mixing of the
genetic material
Nucleic acids are large biomolecules that are crucial in all cells and viruses. They are composed of nucleotides, which are the monomer components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main classes of nucleic aci ...
of a species into new combinations in different individuals. The product of reassortment is called a reassortant. It is particularly used when two similar
virus
A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...
es that are infecting the same cell exchange genetic material. More specifically, it refers to the swapping of entire segments of the genome, which only occurs between viruses with segmented genomes. (All known viruses with segmented genomes are RNA viruses.)
Flu virus
The classical example of reassortment is seen in the
influenza viruses
''Orthomyxoviridae'' () is a family of negative-sense RNA viruses. It includes nine genera: '' Alphainfluenzavirus'', '' Betainfluenzavirus'', '' Gammainfluenzavirus'', '' Deltainfluenzavirus'', '' Isavirus'', '' Mykissvirus'', '' Quaranjavir ...
, whose genomes consist of eight distinct segments of RNA. These segments act like mini-chromosomes, and each time a flu virus is assembled, it requires one copy of each segment.
If a single host (a human, a chicken, or other animal) is infected by two different strains of the influenza virus, then it is possible that new assembled viral particles will be created from segments whose origin is mixed, some coming from one strain and some coming from another. The new reassortant strain will share properties of both of its parental lineages.
Reassortment is responsible for some of the major
antigenic shift
Antigenic shift is the process by which two or more different strains of a virus, or strains of two or more different viruses, combine to form a new subtype having a mixture of the surface antigens of the two or more original strains. The term is ...
s in the history of the influenza virus. In the 1957 "
Asian flu
Asian may refer to:
* Items from or related to the continent of Asia:
** Asian people, people in or descending from Asia
** Asian culture, the culture of the people from Asia
** Asian cuisine, food based on the style of food of the people from As ...
" and 1968 "
Hong Kong flu
The Hong Kong flu, also known as the 1968 flu pandemic, was an influenza pandemic that occurred between 1968 and 1970 and which killed between one and four million people globally. It is among the deadliest pandemics in history, and was caus ...
"
pandemic
A pandemic ( ) is an epidemic of an infectious disease that has a sudden increase in cases and spreads across a large region, for instance multiple continents or worldwide, affecting a substantial number of individuals. Widespread endemic (epi ...
s, flu strains were caused by reassortment between an avian virus and a human virus. In addition, the
H1N1
Influenza A virus subtype H1N1 (A/H1N1) is a subtype of influenza A virus (IAV). Some human-adapted strains of H1N1 are endemic in humans and are one cause of seasonal influenza (flu). Other strains of H1N1 are endemic in pigs ( swine influen ...
virus responsible for the
2009 swine flu pandemic
The 2009 swine flu pandemic, caused by the H1N1/swine flu/influenza virus and declared by the World Health Organization (WHO) from June 2009 to August 2010, was the third recent flu pandemic involving the H1N1 virus (the first being the 1918â ...
has an unusual mix of swine, avian and human influenza genetic sequences.
Multiplicity reactivation
When
influenza viruses
''Orthomyxoviridae'' () is a family of negative-sense RNA viruses. It includes nine genera: '' Alphainfluenzavirus'', '' Betainfluenzavirus'', '' Gammainfluenzavirus'', '' Deltainfluenzavirus'', '' Isavirus'', '' Mykissvirus'', '' Quaranjavir ...
are inactivated by
UV irradiation or
ionizing radiation
Ionizing (ionising) radiation, including Radioactive decay, nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionization, ionize atoms or molecules by detaching ...
, they remain capable of multiplicity reactivation in infected host cells. If any of a virus's
genome
A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...
segments is damaged in such a way as to prevent replication or expression of an essential
gene
In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
, the virus is inviable when it, alone, infects a host cell (single infection). However, when two or more damaged viruses infect the same cell (multiple infection), the infection can often succeed (multiplicity reactivation) due to reassortment of segments, provided that each of the eight genome segments is present in at least one undamaged copy.
[Michod RE, Bernstein H, Nedelcu AM. Adaptive value of sex in microbial pathogens. Infect Genet Evol. 2008 May;8(3):267-85. doi: 10.1016/j.meegid.2008.01.002. Epub 2008 Jan 16. Review. ]
Other viruses
The
reptarenavirus family, responsible for
inclusion body disease
Inclusion body disease (IBD) is an infectious and invariably fatal viral disease affecting captive specimens of the boid family of snakes, particularly ''Boa constrictor
The boa constrictor (scientific name also ''Boa constrictor''), also know ...
in snakes, shows a very high degree of genetic diversity due to reassortment of genetic material from multiple strains in the same infected animal.
See also
* Other kinds of nonhereditary genetic change
**
Antigenic shift
Antigenic shift is the process by which two or more different strains of a virus, or strains of two or more different viruses, combine to form a new subtype having a mixture of the surface antigens of the two or more original strains. The term is ...
**
Horizontal gene transfer
Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between organisms other than by the ("vertical") transmission of DNA from parent to offspring (reproduction). HGT is an important factor in the e ...
*
Genetic recombination
Genetic recombination (also known as genetic reshuffling) is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent. In eukaryot ...
References
History of April-2009 flucollected by
Bionyt
''BioNyt Videnskabens Verden'' (BioNews Science World) is a Danish language popular science magazine published by Foreningen af Yngre Biologer - Biologisk Forum. The magazine was launched in 1980 and is currently being published only in Denmark. ...
.
External links
An animation from hhmi.org illustrating the process
*
* Offers a good introduction with figures on the concept of reassortment (as well as recombination).
{{Virus topics
Genetics
Virology
Influenza