Double minute

Double minutes are small fragments of extrachromosomal DNA, which have been observed in a large number of human tumors including breast, lung, ovary and colon. 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.