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Genetic recombination allows specific DNA segments to 'break apart' from the chain, whereby they undergo locational change within the DNA molecule. Basically, two DNA helices split horizontally, and reconnect with their neighbouring pair. This 'recombination' of genetic information alters the structural nature of each DNA molecule, thereby changing the nature of the genetic code stored within the molecule. This process is said to increase the nature of natural selection. Also, this process is what inherently determines the nature of change within sexual reproduction. The chromosone alterations that occur during recombination change the organisms 'biological output' such that the offspring of said organism are chromosonally 'different' from the parents.
The most popular for of genetic recombination, known as homologous recombination, occurs only when the two chromosonal strands (the DNA) share very similar genetic sequences. Non Homologous recombination itself is known to produce various genetic 'dislocations' resulting in various genetic abnormalities and physical mutations.
The recombination reaction occurs when the enzymes referred to as recombinases catalyze the DNA molecule. This involves the 'horizontal' separation of the DNA molecule, where the helix is essentially 'cut' in half, opposite in which it is 'spliced' during transcription or replication. The 'separation' of the DNA helix begins a biological function known as Crossover, involving the reconnection of genetic pieces in a manner that alters the genetic code.
The crossover begins when the recombinases 'nick' the DNA helix in a manner which separates one segment of the helix from the other. This 'nick' in the chain, creates a 'chemical hook' which serves to assist in the reattachment of that segment of DNA to a new segment. The helices, once separated from their other 'halves' connect to a sister pair of partially disconnected helices, whereby the chemical hooks pick up the opposing strands and form a bond with their new partners. This joining process creates what is known as a 'Holiday Junction' (or a cross-strand exchange).
Although there are other forms of recombination, the above mentioned 'homologous recombination' is the most popular. Other forms include: conservative site-specific recombination, where only specific sites on the helix are targeted, rather than a whole section of the helix itself, as well as transpositional recombination, where a 'sister' identical strand is not required for the DNA helix to rejoin after separation.
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