H. Trevor Johnson-Steigelman, assistant professor of physics, will present “Unraveling DNA: How Physics Helped Solve the Structure of DNA” at 9 a.m. Oct. 25 at Finger Lakes Community College, 3325 Marvin Sands Drive, Hopewell.

Johnson-Steigelman will explain how James Watson and Francis Crick determined the chemical composition of DNA, but couldn’t figure out how it could accomplish genetic feats known by biologists. Rosalind Franklin, a chemist and X-ray crystallographer, used X-ray diffraction to find clues that led to the discovery of the double helix.

The free presentation will include a laser to demonstrate diffraction and identify the key features in DNA’s diffraction pattern. For more information, call 585-785-1623.