Question: How are the genetic material of some viruses formed?
About the article "RNA", section "Double-stranded RNA".

Candidate passages:
All viruses bind to their hosts and introduce their genetic material into the host cell as part of their replication cycle.
This genetic material contains basic 'instructions' of how to produce more copies of these viruses, hacking the body's normal production machinery to serve the needs of the virus.
The host cell will carry out these instructions and produce additional copies of the virus, leading to more and more cells becoming infected.
Some types of viruses insert their genome into the host's cytoplasm, but do not actually enter the cell.
Others penetrate the cell membrane disguised as protein molecules and enter the cell.
There are two main types of virus infection: lytic and lysogenic.
Shortly after inserting its DNA, viruses of the lytic cycle quickly produce more viruses, burst from the cell and infect more cells.
Lysogenic viruses integrate their DNA into the DNA of the host cell and may live in the body for many years before responding to a trigger.
The virus reproduces as the cell does and does not inflict bodily harm until it is triggered.
The trigger releases the DNA from that of the host and employs it to create new viruses. 
Bacteriophages, the viruses which infect bacteria, can be relatively easily grown as viral plaques on bacterial cultures.
Bacteriophages occasionally move genetic material from one bacterial cell to another in a process known as transduction, and this horizontal gene transfer is one reason why they served as a major research tool in the early development of molecular biology.
The genetic code, the function of ribozymes, the first recombinant DNA and early genetic libraries were all arrived at using bacteriophages.
Certain genetic elements derived from viruses, such as highly effective promoters, are commonly used in molecular biology research today.
Growing animal viruses outside of the living host animal is more difficult.
Classically, fertilized chicken eggs have often been used, but cell cultures are increasingly employed for this purpose today.
Since some viruses that infect eukaryotes need to transport their genetic material into the host cell's nucleus, they are attractive tools for introducing new genes into the host (known as transformation or transfection).
Modified retroviruses are often used for this purpose, as they integrate their genes into the host's chromosomes.
This approach of using viruses as gene vectors is being pursued in the gene therapy of genetic diseases.
An obvious problem to be overcome in viral gene therapy is the rejection of the transforming virus by the immune system.
Phage therapy, the use of bacteriophages to combat bacterial diseases, was a popular research topic before the advent of antibiotics and has recently seen renewed interest.
Oncolytic viruses are viruses that preferably infect cancer cells.
While early efforts to employ these viruses in the therapy of cancer failed, there have been reports in 2005 and 2006 of encouraging preliminary results. 
Double-stranded RNA (dsRNA) is RNA with two complementary strands, similar to the DNA found in all cells.
dsRNA forms the genetic material of some viruses (double-stranded RNA viruses).
Double-stranded RNA such as viral RNA or siRNA can trigger RNA interference in eukaryotes, as well as interferon response in vertebrates.
A virus is a small infectious agent that replicates only inside the living cells of other organisms.
Viruses can infect all types of life forms, from animals and plants to bacteria and archaea.
Since Dmitri Ivanovsky's 1892 article describing a non-bacterial pathogen infecting tobacco plants, and the discovery of the tobacco mosaic virus by Martinus Beijerinck in 1898, about 5,000 viruses have been described in detail, although there are millions of different types.
Viruses are found in almost every ecosystem on Earth and are the most abundant type of biological entity.
The study of viruses is known as virology, a sub-speciality of microbiology.
Virus particles (known as virions) consist of two or three parts: i) the genetic material made from either DNA or RNA, long molecules that carry genetic information; ii) a protein coat that protects these genes; and in some cases iii) an envelope of lipids that surrounds the protein coat when they are outside a cell.
The shapes of viruses range from simple helical and icosahedral forms to more complex structures.
The average virus is about one one-hundredth the size of the average bacterium.
Most viruses are too small to be seen directly with an optical microscope.
The origins of viruses in the evolutionary history of life are unclear: some may have evolved from plasmids—pieces of DNA that can move between cells—while others may have evolved from bacteria.
In evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity.
Viruses are considered by some to be a life form, because they carry genetic material, reproduce, and evolve through natural selection.
However they lack key characteristics (such as cell structure) that are generally considered necessary to count as life.
Because they possess some but not all such qualities, viruses have been described as "organisms at the edge of life".
Viruses spread in many ways; viruses in plants are often transmitted from plant to plant by insects that feed on plant sap, such as aphids; viruses in animals can be carried by blood-sucking insects.
These disease-bearing organisms are known as vectors.
Influenza viruses are spread by coughing and sneezing.
Norovirus and rotavirus, common causes of viral gastroenteritis, are transmitted by the faecal–oral route and are passed from person to person by contact, entering the body in food or water.
HIV is one of several viruses transmitted through sexual contact and by exposure to infected blood.
The range of host cells that a virus can infect is called its "host range".
This can be narrow or, as when a virus is capable of infecting many species, broad.
Viral infections in animals provoke an immune response that usually eliminates the infecting virus.
Immune responses can also be produced by vaccines, which confer an artificially acquired immunity to the specific viral infection.
However, some viruses including those that cause AIDS and viral hepatitis evade these immune responses and result in chronic infections.
Antibiotics have no effect on viruses, but several antiviral drugs have been developed. 
The Tymovirales are a newly established order of viruses in the 2009 classification with four genera.
This group consists of viruses which have (+) sense single stranded RNA genomes without DNA intermediates.
Their genetic material is protected by a special coat protein.