Perhaps they include the weight of stuff like histones [1], which DNA is wound up upon in order not to get entangled. That could add some considerable weight. A

Perhaps they include the weight of stuff like histones [1], which DNA is wound up upon in order not to get entangled. That could add some considerable weight. Also there are various epigenetic modifications on top of that, further adding weight, in DNA in its biological form. [1] https://en.wikipedia.org/wiki/Histone https://en.wikipedia.org/wiki/Histone