Reassortment is the mixing of the

genetic material Nucleic acids are biopolymers, macromolecules, essential to all known forms of life. They are composed of nucleotides, which are the monomers made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main cla ...

of a species into new combinations in different individuals. Several different processes contribute to reassortment, including assortment of chromosomes, and

chromosomal crossover Chromosomal crossover, or crossing over, is the exchange of genetic material during sexual reproduction between two homologous chromosomes' non-sister chromatids that results in recombinant chromosomes. It is one of the final phases of geneti ...

. It is particularly used when two similar

virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's 1 ...

es that are infecting the same cell exchange genetic material. In particular, reassortment occurs among

influenza viruses ''Orthomyxoviridae'' (from Greek language, Greek ὀρθός, ''orthós'' 'straight' + μύξα, ''mýxa'' 'mucus') is a family of negative-sense single-stranded RNA virus, negative-sense RNA viruses. It includes seven genus, genera: ''Influenza ...

, 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 genetic shifts 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 Asi ...

" and 1968 "

Hong Kong flu The Hong Kong flu, also known as the 1968 flu pandemic, was a flu pandemic whose outbreak in 1968 and 1969 killed between one and four million people globally. It is among the deadliest pandemics in history, and was caused by an H3N2 strain of ...

pandemic A pandemic () is an epidemic of an infectious disease that has spread across a large region, for instance multiple continents or worldwide, affecting a substantial number of individuals. A widespread endemic (epidemiology), endemic disease wi ...

s, flu strains were caused by reassortment between an avian virus and a human virus. In addition, the

H1N1 In virology, influenza A virus subtype H1N1 (A/H1N1) is a subtype of influenza A virus. Major outbreaks of H1N1 strains in humans include the Spanish flu, the 1977 Russian flu pandemic and the 2009 swine flu pandemic. It is an orthomyxovirus ...

virus responsible for the

2009 swine flu pandemic The 2009 swine flu pandemic, caused by the H1N1 influenza virus and declared by the World Health Organization (WHO) from June 2009 to August 2010, is the third recent flu pandemic involving the H1N1 virus (the first being the 1918–1920 Span ...

has an unusual mix of swine, avian and human influenza genetic sequences. The reptarenavirus family, responsible for inclusion body disease in snakes, shows a very high degree of genetic diversity due to reassortment of genetic material from multiple strains in the same infected animal.

Multiplicity reactivation

When

are inactivated by UV irradiation or

ionizing radiation Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...

, they remain capable of multiplicity reactivation in infected host cells. If any of a virus’s

genome In the fields of molecular biology and genetics, 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 ge ...

segments is damaged in such a way as to prevent replication or expression of an essential

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

, 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.

References

History of April-2009 flu
collected 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 Denmar ...

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

Multiplicity reactivation

See also

References

External links