DNA that is translocated but seemingly without loss of the same DNA in the original location.
The reason I describe this in terms of translocation is that indeed translocation can be the mechanism of chromosomal duplication. That is, DNA from some other location becomes associated with a chromosome or genome, with that chromosome from which the DNA came no longer present within the genome (e.g., as can happen during meiosis, but also as can happen in the course of horizontal gene transfer more generally). The result is that there 'suddenly' are more copies of a given sequence than their had been before, giving the appearance that a piece of DNA had been duplicated.
Chromosomal duplication is the means by which genomes increase in gene number and therefore complexity. The fate of the duplicated DNA, assuming that it does not result in substantial selection against the harboring cell or organism, is either genetic deterioration of one of the gene copies (the 'extra' copy), resulting in the formation of pseudogenes, or instead a divergence in the function of the genes from each other.
On the other hand, a number of genes exist in multiple copies within genomes such as the genes encoding the various ribosomal RNAs. These 'extra' copies presumably exist as a consequence of chromosomal duplication.
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