In the past, making an animal with multiple genetic changes usually required creating separate animals with single changes and then crossbreeding them to produce offspring with multiple changes. With Crispr, multiple genetic changes can be made in one step, by putting multiple guide RNAs into the cell.

“It just completely changes the landscape,” Dr. Doudna said. Berkeley scientists used to farm out that work to specialized laboratories or companies. Now, she said, “people are able to make mice in their own labs.”