NCB2K, Wikipedia has a pretty good discussion of viral recombination: "Antigenic shift, or reassortment, can result in novel and highly pathogenic strains of human viruses. Viruses undergo genetic change by several mechanisms. These include a process called genetic drift where individual bases in the DNA or RNA mutate to other bases. Most of these point mutations are "silent"—they do not change the protein that the gene encodes—but others can confer evolutionary advantages such as resistance to antiviral drugs. Antigenic shift is where there is a major change in the genome of the virus. This occurs as a result of recombination or reassortment. When this happens with influenza viruses, pandemics may result.
Genetic recombination is the process by which a strand of DNA is broken and then joined to the end of a different DNA molecule. This can occur when viruses infect cells simultaneously [each of the virus' DNA strands break apart and recombine with each other]and studies of viral evolution have shown that recombination has been rampant in the species studied. Recombination is common to both RNA and DNA viruses.
"Recombinant DNA" is a form of DNA that does not exist naturally, which is created by combining DNA sequences that would not normally occur together. Recombinant DNA (designated: rDNA) is introduced through the addition of relevant DNA into an existing organismal DNA to code for or alter different traits for a specific purpose, such as antibiotic resistance. It differs from genetic recombination, in that it does not occur through processes within the cell, but is engineered. A recombinant protein is protein that is derived from recombinant DNA.
The Recombinant DNA technique was first proposed by Peter Lobban, a graduate student at Stanford University Department of Biochemistry...a method to isolate and amplify genes or DNA segments and insert them into another cell with precision, creating a transgenic bacterium. Recombinant DNA technology was made possible by the discovery, isolation and application of restriction endonucleases [enzymes that can specifically break DNA/RNA chains at specific points] by Werner Arber, Daniel Nathans, and Hamilton Smith, for which they received the 1978 Nobel Prize in Medicine.
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