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Most DNA in an individual genome is found in chromosomes contained in the nucleus. Multiple forms of extrachromosomal DNA exist, and, while some of these serve important biological functions, [1] they can also play a role in diseases such as cancer. [2] [3] [4]
Extrachromosomal circular DNA (eccDNA) is a type of double-stranded circular DNA structure that was first discovered in 1964 by Alix Bassel and Yasuo Hotta. [1] In contrast to previously identified circular DNA structures (e.g., bacterial plasmids, mitochondrial DNA, circular bacterial chromosomes, or chloroplast DNA), eccDNA are circular DNA found in the eukaryotic nuclei of plant and animal ...
The term plasmid was coined in 1952 by the American molecular biologist Joshua Lederberg to refer to "any extrachromosomal hereditary determinant." [11] [12] The term's early usage included any bacterial genetic material that exists extrachromosomally for at least part of its replication cycle, but because that description includes bacterial viruses, the notion of plasmid was refined over time ...
For example, ncl-1, located in chromosomal DNA, exhibits a larger nucleolus than the wild-type allele, which is in the array. Thus, cells which exhibit larger nucleoli have usually not retained the extrachromosomal array. The gene of interest is the target of the mosaic analysis. Cells lacking the extrachromosomal array also lack the functional ...
Double minutes (DMs) are small fragments of extrachromosomal DNA, which have been observed in a large number of human tumors including breast, lung, ovary, colon, and most notably, neuroblastoma. They are a manifestation of gene amplification as a result of chromothripsis , [ 1 ] during the development of tumors, which give the cells selective ...
Circular extrachromosomal DNA are not only found in yeast but other eukaryotic organisms. [15] [16] A regulated formation of eccDNA in preblastua Xenopus embryos has been developed. The population of circular rDNA is decreased in embryos, indicative of the circular rDNA migrating to linear DNA, as was shown in their analysis on 2D gel ...
CGH was originally developed to observe chromosomal aberrations in tumour cells. This method uses two genomes, a sample and a control, which are labeled fluorescently to distinguish them. [5] In CGH, DNA is isolated from a tumour sample and biotin is attached. Another labelling protein, digoxigenin, is attached to the reference DNA sample. [6]
The ability for mammals to tolerate aneuploidies in the sex chromosomes arises from the ability to inactivate them, which is required in normal females to compensate for having two copies of the chromosome. Not all genes on the X chromosome are inactivated, which is why there is a phenotypic effect seen in individuals with extra X chromosomes.