You cant use any old microscope
Many scientists use electron, scanning tunneling and atomic force microscopes to view individual DNA molecules,” said Michael W. Davidson, curator of the National High Magnetic Field Laboratory at Florida State University. “But even with these advanced technologies, DNA appears as a string rather than being resolvable into the individual units from which it is composed.”
New techniques are allowing the imaging of DNA with conventional optical microscopes as well, he said, but they are in their infancy.
Chromosomes, the spiraling strands of DNA that package the series of chemical bits called genes, are easily visible through a strong enough microscope if the right stain is used. In fact, the development in the 19th century of aniline dyes that make the chromosomes stand out led to their discovery. The name is derived from chromatin, meaning the part of the cell nucleus that is easily dyed.
Chromosomes are best seen at the point in cell division called the metaphase stage of mitosis. At this stage, the strands are condensed and aligned in one plane. But a chromosome can contain tens of thousands of genes, and the tiny details that make the difference between the DNA of two individual people are not visible through a microscope.
