By Patricia Sellers
October 22, 2013

FORTUNE — When Marissa Mayer landed at Yahoo

as its new CEO 15 months ago, some employees told her, “There are 1,000 things you need to fix.”

“It’s really overwhelming when people come up and say that to you because, how are you going to fix 1,000 things?” she said on stage last Thursday at the Fortune Most Powerful Women Summit.

What enabled Mayer to fix 1,000 things was a piece of advice she got from Eric Schmidt, her former boss at Google

. “Eric says that good executives confuse themselves when they convince themselves that they actually do things. It’s your job to be defense [rather than] offense. Clear the path. Get obstacles out of the way”—and then let employees run “as far and fast as they can.”

MORE: Fortune’s Most Powerful Women Summit

A self-proclaimed geek, Mayer translated Schmidt’s advice into her own science-based theory of leadership. She told the MPW audience—including Warren Buffett

and Xerox

chief Ursula Burns—that she thinks of culture as DNA. “I don’t know a lot about genetics, but I know a bit,” Mayer said. “You want the genes that are positive to hyper-express themselves.”

To motivate Yahoo’s 12,000 employees around the world, Mayer says she’s tried to “take some of the negative genes that are getting in the way and shut them off. It’s not about injecting new mutant DNA. It’s not about changing the culture. It’s about making the culture the best version of itself.”

Her tactic has been a program she launched called PB&J, which is designed to rid Yahoo of poisonous processes, useless bureaucracy and jams. As part of PB&J, Mayer and her new management team created an online tool to collect employee complaints and employee votes on whether the problems are worth trying to fix. Any complaint—such as underpowered laptops or onerous rules at the company gym—that generates at least 50 votes gets management attention–and the onus on the rank and file to fix the problem. Employees get evaluated on how they do that.

One year in, Mayer reported at the Summit, “We fixed 1000 things, some big, some small.”

The cultural overhaul clearly is making Yahoo a more attractive place to work. Last quarter, Mayer says, the company received resumes from 17,000 job applicants. That’s up from 2,000 last year. Here’s my full interview with Mayer at the MPW Summit:

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