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Double minutes 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 during the development of tumors, which give the cells selective advantages for growth and survival. They frequently harbor amplified oncogenes and genes involved in drug resistance. Double minutes, like actual chromosomes, are composed of chromatin and replicate in the nucleus of the cell during cell division. Unlike typical chromosomes, they are composed of circular fragments of DNA, up to only a few million base pairs in size and contain no centromere or telomere.

References

• Baskin, F; Rosenberg, RN; Dev, V (June 1981). "Correlation of double-minute chromosomes with unstable multidrug cross-resistance in uptake mutants of neuroblastoma cells". Proc Natl Acad Sci U S A 78 (6): 3654-3658. PMID 6943568. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC319629/.   Free full-text.

• Barker PE (February 1982). "Double minutes in human tumor cells". Cancer genetics and cytogenetics 5 (1): 81–94. PMID 6175392. http://linkinghub.elsevier.com/retrieve/pii/0165-4608(82)90043-7.  

• Masters, J; Keeley, B; Gay, H; Attardi, G (1982). "Variable content of double minute chromosomes is not correlated with degree of phenotype instability in methotrexate-resistant human cell lines". Mol Cell Biol. PMID 7110138. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC369819/.   Free full-text.