A few months ago I got in my car and drove north until I reached a remarkable building filled with several million mice. At Jackson Laboratory in Bar Harbor, Maine, scientists are studying mice to understand many mysteries of genetics and medicine. But I was particularly curious about a project that they’ve only recently launched: an attempt to understand how many genes working together give rise to complex traits. When those complex traits go awry, the result may be a common disease such as heart disease, diabetes, or cancer. The article I wrote about what I learned, “Mendel’s Mouse,” appears in the May issue of Discover. Discover posted the story today on their web site, where you can read