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Recombination

Recombination

Recombination, is a process during which genetic material is shuffled during reproduction to form new combinations. This mixing is important from an evolutionary standpoint because it allows the expression of different traits between generations. The process involves a physical exchange of nucleotides between duplicate strands of deoxyribonucleic acid (DNA ).

There are three types of recombination; homologous recombination, specific recombination and transposition . Each type occurs under different circumstances. Homologous recombination occurs in eukaryotes , typically during the first phase of the meiotic cell division cycle. In most eukaryotic cells, genetic material is organized as chromosomes in the nucleus . A nick is made on the chromosomal DNA of corresponding strands and the broken strands cross over, or exchange, with each other. The recombinant region is extended until a whole gene is transferred. At this point, further recombination can occur or be stopped. Both processes require the creation of another break in the DNA strand and subsequent sealing of the nicks by special enzymes .

Site specific recombination typically occurs in prokaryotes. It is the mechanism by which viral genetic material is incorporated into bacterial chromosomes. The event is site-specific, as the incorporation (integration) of viral genetic material occurs at a specific location on the bacterial genome, called the attachment site, which is homologous with the phage genome. Under appropriate conditions alignment and merging of the viral and bacterial genomes occurs.

Transposition is a third type of recombination. It involves transposable elements called transposons . These are short segments of DNA found in both prokaryotes and eukaryotes, which contain the information enabling their movement from one genome to another, as well as genes encoding other functions. The movement of a transposon, a process of transposition, is initiated when an enzyme cuts DNA at a target site. This leaves a section that has unpaired nucleotides. Another enzyme called transposase facilitates insertion of the transposon at this site. Transposition is important in genetic engineering, as other genes can be relocated along with the transposon DNA. As well, transposition is of natural significance. For example, the rapid reshuffling of genetic information possible with transposition enables immunocytes to manufacture the millions of different antibodies required to protect eukaryotes from infection.

See also Cell cycle (eukaryotic), genetic regulation of; Cell cycle (prokaryotic), genetic regulation of; Microbial genetics

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"Recombination." World of Microbiology and Immunology. . Encyclopedia.com. 23 Oct. 2017 <http://www.encyclopedia.com>.

"Recombination." World of Microbiology and Immunology. . Encyclopedia.com. (October 23, 2017). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/recombination

"Recombination." World of Microbiology and Immunology. . Retrieved October 23, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/recombination

recombination

recombination, process of "shuffling" of genes by which new combinations can be generated. In recombination through sexual reproduction, the offspring's complete set of genes differs from that of either parent, being rather a combination of genes from both parents. In recombination by crossing over, alleles of genes are exchanged between homologous chromosomes during meiosis. This exchange results in the generation of new combinations of alleles on segments of chromosomes, counteracting the tendency of linked genes, i.e., genes on the same chromosome, to be always transmitted as a group. Various mechanisms for introducing new genetic material have been discovered in bacteria. These mechanisms have been used extensively to study gene structure and function. In transformation, a fragment of free deoxyribonucleic acid (DNA) is inserted in a recipient bacterium (see nucleic acid). The free DNA fragment comes from the chromosome of a bacterial cell that has been lysed, or dissolved. In transduction, genetic material is transferred from one bacterium to another by a carrier virus. When a virus enters a bacterium, its DNA can be inserted into the bacterial chromosome, reproducing along with the host chromosome in cell division. Subsequently, sometimes many bacterial generations later, the viral genetic material may detach from the bacterial chromosome, taking some of the bacterial chromosomal material along with it. The bacterium then lyses, the viral particle enters a new bacterium, and the viral particle, together with the bacterial genes it carries, is inserted into the chromosome of the new host. In conjugation, which occurs between bacteria of the same species and also between some bacteria of different species, either an entire chromosome or a part of one is transferred from a bacterium of a donor-mating strain to a bacterium of a recipient-mating strain. Donor strains, denoted male, contain a sex-factor particle composed of a nucleic acid; recipient, or female, strains lack the particle (see episome). Conjugation has been used to construct genetic maps, i.e., the ordering of genes along a chromosome. Evidence from transformation experiments was used to support the idea that DNA was the genetic material.

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"recombination." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 23 Oct. 2017 <http://www.encyclopedia.com>.

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recombination

recombination The rearrangement of genes that occurs when reproductive cells (gametes) are formed. It results from the independent assortment of parental sets of chromosomes and exchange of chromosomal material (see crossing over) that occur during meiosis. Recombination results in offspring that have a combination of characteristics different from that of their parents. Recombination can also be induced artificially by genetic engineering techniques.

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"recombination." A Dictionary of Biology. . Encyclopedia.com. 23 Oct. 2017 <http://www.encyclopedia.com>.

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recombination

re·com·bi·na·tion / rēˌkəmbəˈnāshən/ • n. the process of recombining things. ∎  Genetics the rearrangement of genetic material, esp. by crossing over in chromosomes or by the artificial joining of segments of DNA from different organisms.

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"recombination." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 23 Oct. 2017 <http://www.encyclopedia.com>.

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recombination

recombination The arrangement of genes in offspring in combinations that differ from those in either parent, and the assortment of chromosomes into new sets.

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"recombination." A Dictionary of Plant Sciences. . Encyclopedia.com. 23 Oct. 2017 <http://www.encyclopedia.com>.

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recombination

recombination The arrangement of genes in offspring in combinations that differ from those in either parent, and the assortment of chromosomes into new sets.

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"recombination." A Dictionary of Zoology. . Encyclopedia.com. 23 Oct. 2017 <http://www.encyclopedia.com>.

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recombination

recombination The exchange of DNA between molecules, resulting in the formation of new sequences.

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"recombination." A Dictionary of Ecology. . Encyclopedia.com. 23 Oct. 2017 <http://www.encyclopedia.com>.

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"recombination." A Dictionary of Ecology. . Retrieved October 23, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/recombination