The salarians believed the genophage would be used as a deterrent, a position the turians viewed as naive. Once the project was complete, the turians mass produced and deployed it. The krogan homeworld, their colonies, and all occupied worlds were infected.
Talk to the salarian about his previous work with the krogan genophage. Mordin was very involved in the genophage. He knows an awful lot about it—perhaps too much.
Dalatrass: No good can come from curing the genophage. / Shepard: The krogan have paid for their mistakes. The genophage has gone on long enough. / Wrex: One thousand, four hundred and seventy-six years, if you're keeping track. / Datatrass: It was a thousand years of peace free from these... brutes.
2013 May 15, Sebastian Alvarado, “Here's How Mass Effect's Biological Warfare is Scientifically Possible”, in Kotaku[2], archived from the original on 12 June 2014, Science and Video Games:
Mass Effect’sgenophage is one of the few fictions in gaming that is easiest to match to real science.[…] In Mass Effect, the genophage was a Salarian-engineered virus capable of sterilizing the entire Krogan population.
2021 June 4, Jhaan Elker, “Every ‘Mass Effect’ squadmate, ranked from a storytelling perspective”, in The Washington Post[3], →ISSN, →OCLC, archived from the original on 04 June 2021, Launcher News[4]:
Mordin didn’t create the Genophage, but he maintains it, making sure it continues to be effective, wrecking any chance of true Krogan civilizational growth. He doesn’t regret this decision, passionately arguing that the Genophage was a necessary choice to protect the galaxy from Krogan brutality. He is a great counterpoint to the emotional connection players formed with Wrex in the previous game, and his lovable goofiness makes it difficult for players to decide where they land on the Genophage.
2022 July 26, Mac Schwerin, “Why I Care More About Nonplayer Characters Than About Some Ex-Lovers”, in The New York Times[5], →ISSN, →OCLC, archived from the original on 26 July 2022, Letter of Recommendation[6]:
That’s the paradox of good single-player gaming. Though you are the main character, the NPCs take center stage. Their needs provide direction. Not surprisingly, I’ve always gravitated toward them in times of aimlessness: long, empty afternoons, or after a breakup or a layoff. When I’m jonesing for a quick hit of purpose, there’s Karen, asking me to help pick the grapes in her vineyard. There’s Wrex, asking me to help him cure the widespread infertility among his people owing to the long-ago deployment of a biological weapon called the genophage. Together we’ll accomplish something, and then I get to walk away.
