The organization of the human genome is wellknown, with the archetypal image of DNA bundled up in 23 pairs of chromosomes.
But something evades this highly ordered picture. For half a century researchers have been puzzled by the existence of what is now known as not extraterrestrial but extrachromosomal circular DNA (eccDNA). Small loops of DNA that floats around along their heavily chromatin-folded counterparts.
Circular DNA is highly abundant in cancer cells and is a common trait of many types of cancers. They have been shown to carry cancer-promoting genes and the mere shape of them, seem to incite aggresive growth and drug resistance.
Scientists can see extrachromosomal DNA (small circles) under the microscope only when the rest of a cell’s DNA is condensed into chromosomes as a cell is getting ready to divide. The chromosomes are evenly divided into daughter cells, but the distribution of ecDNA is random.