Near the end of Mordin’s Loyalty mission Old Blood, you have the choice to keep or destroy Maelon’s research data. This will have consequences for Mass Effect 3.
Choice: Keep or Destroy Maelon’s Data
Near the end of Mordin’s Loyalty mission Old Blood, you’ll enter Maelon’s Lab, here, you’ll get a scene of Maleon scanning a holo screen with an Omni-Tool, Mordin will confront him, and Maelon will tell him his hands are already bloody, but it’s worth it, if it can undo the genophage, mainly because he sees the Galaxy better off with the Krogan than without them. Once that’s been dealt with, you’ll have the choice on what should happen to the data, and the choice you make here will have direct consequences for a character in Mass Effect 3.
Destroy the data
In the event of destroying the data, Eve, will die in the mission Priority Tuchanka in Mass Effect 3. Also, if Wrex wasn’t recruited in Mass Effect 1 or if he was sacrificed on Virmire, you’ll get the chance to save Mordin, and you’ll be able to sabotage the genophage cure, and convince the doctor to walk away with their life still intact in Mass Effect 3.
Keep the data
If you decide to keep the data, Eve will survive during Priority Tuchanka in Mass Effect 3, but this will make it impossible to cure the genophage without killing the Doctor present. Also, Mordin will sacrifice himself during the dispersal of the Genophage cure, or you (Shepard) will kill him.