During the Mission Priority Mars, you’ll be accompanied by the survivor from the Mission: Virmire Assault, which’ll be either Ashley or Kaidan.
Choice: Paragon or Renegade
Throughout the Mission Priority Mars, you’ll have Paragon or Renegade choices to make, depending on what you chose, will reflect later in the game on how they act towards you.
If you mainly picked Paragon actions, Ashley or Kaidan will be more likely to side with you at the end of the Mission: Priority Citadel.
If you mainly picked Renegade actions, Ashley or Kaidan will require a persuasion check on whether they trust you or not at the end of the Mission: Priority Citadel. Depending on how many Renegade actions you chose, you may be required to kill them to end the mission.