Since the two chains in our model are intertwined,it is essential for them to untwist if they are to separate. As they meke ono complete turn around each other in 34 A. them will be about 150 turns er million moleculer weight, so that whatever the precise structure of the chromosome a considerable amount of uncoiling would be necessary. It is well known from microscopic observation that much coiling and uncoiling occurs during mitosis, and though this is on a much Iarger scale it probably reflects similar processes on a molecular level. Although it is difflcult at the moment to see how
these proesses occur without everything getting tangled, we do not feel that this objection will be insuperable.