In complex cells, the genetic material--DNA--is
stored in the nucleus, which serves as the cell's
control center. When a cell is not dividing,
DNA strands look like a ball of entangled threads.
But when the cell divides, the DNA strands duplicate
and take on the complicated organization of chromosomes.
Most bacteria have only one, circular chromosome;
but a more complex organism like the Indian fern (Ophioglossum
reticulatum), has over 1200. Scientists
are using high-powered microscopes to see inside
the nucleus of dividing cells to determine what
role different DNA arrangements play in cell
division and other functions.