In her San Francisco dining room lab, for example, 31-year-old computer programmer Meredith L. Patterson is trying to develop genetically altered yogurt bacteria that will glow green to signal the presence of melamine, the chemical that turned Chinese-made baby formula and pet food deadly.

She learned about genetic engineering by reading scientific papers and getting tips from online forums. She ordered jellyfish DNA for a green fluorescent protein from a biological supply company for less than $100. And she built her own lab equipment, including a gel electrophoresis chamber, or DNA analyzer, which she constructed for less than $25, versus more than $200 for a low-end off-the-shelf model.