Mass Effect 3/Turians, Salarians and Krogans

You'll meet them in a space area for a meeting. This is the dividing factor as it's worth mentioning that the salarian councilor is hostile to the genophage cure and the krogans. So it's simply being on the side of the krogan or sacrificing the krogan for the salarians but the surprise decision would come later.

Meet EDI
If you haven't done so, go to the doctor area and go in. The fire and smoke ended and it turns out that EDI is in Dr Eve's body. Of course of the affection from Joker, it's revealed that he removed the shackles that allows EDI to have her own free will. To know more about EDI, she's basically a robotic computer and can be quite hard to get the grasp because she's gathering data but she's also now your squad mate.

Saving the female krogan
This level is straight forward. For more details, assuming you have Wrex coming along to the science centre. A quick backstory, if you save Wrex, he'll be more gung ho in seeing through the alliance. But if you have killed Wrex, Wreav instead will take his place with a more tame approach. The same goes with Mordin. If Mordin has died in a suicide mission, Padok Wiks takes over his role.