Humans have 46 chromosomes, and each one is capped at either end by repetitive sequences called telomeres. If you ask a biologist if humans have circular DNA, they are likely to say ‘no.’ That is because eukaryotic cell nuclei have linear chromosomes, while prokaryotes have circular nucleoids and plasmids. However, biologists also know that most of our cells have mitochondria that do, in fact, retain the circular DNA, the chromosome ‘M,’ which they inherited from their prokaryotic ancestors.