Mitochondria have their own small circular DNA, inherited only from your mother. They are thought to descend from ancient bacteria absorbed by our ancestors' cells.
Packed into a nucleus a few micrometres wide, your DNA is wound and coiled with astonishing efficiency. Stretched end to end, the DNA in your whole body would reach far beyond the Sun.
Rosalind Franklin's X-ray image, known as Photo 51, showed the unmistakable X pattern of a double helix. It took a hundred hours of exposure and settled the structure of life itself.
