Genetic recombination is the process by which a strand of the genetic material (usually DNA; but can also be RNA) is broken and then joined to the end of a different DNA molecule. In eukaryotes recombination commonly occurs during meiosis as chromosomal crossover between paired chromosomes. This process leads to offspring having different combinations of genes from their parents and can produce new chimeric alleles. In evolutionary biology this shuffling of genes is thought to have many advantages, including that of allowing sexually reproducing organisms to avoid Muller's ratchet. However, a recombination pathway in DNA is any way by which a broken DNA molecule is reconnected to form a whole DNA strand. The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... Left: An RNA strand, with its nitrogenous bases. ... Kingdoms Eukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. ... For the figure of speech, see meiosis (figure of speech). ... Thomas Hunt Morgans illustration of crossing over (1916) Homologous Recombination is the process by which two chromosomes, paired up during prophase I of meiosis, exchange some distal portion of their DNA. Crossover occurs when two chromosomes, normally two homologous instances of the same chromosome, break and then reconnect but... An allele is any one of a number of alternative forms of the same gene occupying a given locus (position) on a chromosome. ... In evolutionary genetics, Mullers ratchet (named after Hermann Joseph Muller and a mechanical device) is the name given to the process by which the genomes of an asexual population accumulate deleterious mutations in an irreversible manner. ...

In molecular biology "recombination" can also refer to artificial and deliberate recombination of disparate pieces of DNA, often from different organisms, creating what is called recombinant DNA. Molecular biology is the study of biology at a molecular level. ... Recombinant DNA (rDNA) is an artificial DNA sequence resulting from the combination of different DNA sequences. ...

Enzymes called recombinases catalyze natural recombination reactions. RecA, the recombinase found in E. coli, is responsible for the repair of DNA double strand breaks (DSBs). In yeast and other eukaryotic organisms there are two recombinases required for repairing DSBs. The RAD51 protein is required for mitotic and meiotic recombination and the DMC1 protein is specific to meiotic recombination. Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... Recombinases, genetic recombination enzymes [1], can refer to: Cre recombinase Hin recombinase ^ MeSH Recombinases Category: ... Catalyst redirects here. ... For the village in Slovakia, see Reca. ... E. coli redirects here. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Chromalveolata Protista Alternative phylogeny Unikonta Opisthokonta Metazoa Choanozoa Eumycota Amoebozoa Bikonta Apusozoa Cabozoa Rhizaria Excavata Corticata Archaeplastida Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. ... Rad51 is the eukaryotic homolog of the prokaryotic RecA protein. ... Mitosis divides genetic information during cell division. ... For the figure of speech, see meiosis (figure of speech). ...

Chromosomal crossover

Main article: Chromosomal crossover

Thomas Hunt Morgan's illustration of crossing over (1916)

Chromosomal crossover refers to recombination between the paired chromosomes inherited from each of one's parents, generally occurring during meiosis. During prophase I the four available chromatids are in tight formation with one another. While in this formation, homologous sites on two chromatids can mesh with one another, and may exchange genetic information. Thomas Hunt Morgans illustration of crossing over (1916) Homologous Recombination is the process by which two chromosomes, paired up during prophase I of meiosis, exchange some distal portion of their DNA. Crossover occurs when two chromosomes, normally two homologous instances of the same chromosome, break and then reconnect but... Image File history File links Download high resolution version (1174x910, 65 KB) Summary An early of the genetic phenomenon of crossing over, from Thomas Hunt Morgans 1916 A Critique of the Theory of Evolution, page 132. ... Image File history File links Download high resolution version (1174x910, 65 KB) Summary An early of the genetic phenomenon of crossing over, from Thomas Hunt Morgans 1916 A Critique of the Theory of Evolution, page 132. ... A scheme of a condensed (metaphase) chromosome. ... For the figure of speech, see meiosis (figure of speech). ... For the figure of speech, see meiosis (figure of speech). ... A chromatid forms one part of a chromosome after it has coalesced for the process of mitosis or meiosis. ... In biology, homology is any similarity between structures that is due to their shared ancestry. ...

Because recombination can occur with small probability at any location along chromosome, the frequency of recombination between two locations depends on their distance. Chromosomes are expected to cross over at many points along their length; for genes sufficiently distant on the same chromosome the amount of crossover is so high that these genes effectively assort independently. It has been suggested that this article or section be merged into genetic linkage. ...

Conservative site-specific recombination

Main article: Site-specific recombination

In conservative site-specific recombination, a mobile DNA element is inserted into a strand of DNA by means similar to that seen in crossover. A segment of DNA on the mobile element matches exactly with a segment of DNA on the target, allowing enzymes called integrases to insert the rest of the mobile element into the target. Integrases are a special type of Recombinases. Recombinases are enzymes which cleave the double stranded DNA at specific sites resulting in a loss of the Phosphodiester bonds. This reaction is stabilised by the formation of a covalent bond between the Recombinase and the DNA through a Phospho Tyrosine Bond. // In site-specific-recombination, DNA strand exchange takes place between segments possessing only a limited degree of sequence homology (Kolb 2002; Coates et al. ... // In site-specific-recombination, DNA strand exchange takes place between segments possessing only a limited degree of sequence homology (Kolb 2002; Coates et al. ...

Transpositional recombination

Another form of site-specific recombination, transpositional recombination does not require an identical strand of DNA in the mobile element to match with the target DNA. Instead, the integrases involved introduce nicks in both the mobile element and the target DNA, allowing the mobile DNA to enter the sequence. The nicks are then removed by ligases. In biochemistry, a ligase is an enzyme that can catalyse the joining of two molecules (ligation or glue together) by forming a new chemical bond, with concomitant hydrolysis of ATP or other similar molecules. ...

Nonhomologous recombination

Main article: Non-homologous end joining

Recombination between DNA sequences that contain no sequence homology, also referred to as nonhomologous end joining. Non-homologous end joining (NHEJ) is one pathway that can be used to repair double-stranded DNA breaks. ... In biology, homology is any similarity between structures that is due to their shared ancestry. ... Non-homologous end joining (NHEJ) is one pathway that can be used to repair double-stranded DNA breaks. ...

See also

• Recombination frequency

It has been suggested that this article or section be merged into genetic linkage. ...

External links

• The Holliday Model of Genetic Recombination
• MeSH Genetic+recombination
• Animated guide to homologous recombination.

Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. ...

References

• Alberts, B. et al., Molecular Biology of the Cell, 3rd Edition. Garland Publishing, 1994.
• Mayerhofer R, Koncz-Kalman Z, Nawrath C, Bakkeren G, Crameri A, Angelis K, Redei GP, Schell J, Hohn B, Koncz C. T-DNA integration: a mode of illegitimate recombination in plants. EMBO J. 1991 Mar;10(3):697-704.

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