which often appear as X-shaped structures . At different times during the life cycle of a cell, the DNA that makes up the cell's chromosomes can be tightly compacted into a structure that is ...

Remarkably, the DNA inside all these cells is exactly the same. What makes the cells differ from one another is that different genes in that DNA are either turned on or off in each type of cell.

Chances are you've seen an illustration of DNA's double-helix structure and even pictures of the chromosomes that comprise the human genome. But where and how does the famous double helix fit into ...