There’s no image in biology more iconic than our chromosomes — all 23 pairs of DNA bundles arrayed in a genetic lineup. But in a surprising number of cases, this picture leaves out something very important.

In some cells, extra circles of DNA float alongside the regular chromosomes. Scientists first noticed this so-called extrachromosomal DNA five decades ago. But for years they weren’t exactly sure what to make of it.

New research is now focusing on those mysterious loops. They are surprisingly common in cancer cells and play a bigger role in many types of cancers than was previously recognized. Healthy cells can carry smaller circles of their own. These DNA circles also may affect how our bodies work, and may even be linked to aging or diseases other than cancer.

“I think we’re just opening our eyes up,” said Birgitte Regenberg, a biologist at the University of Copenhagen who has pioneered methods for detecting these circles. She is co-organizing the first meeting on circular DNA, to be held in Berlin in January.