Dominate is an excellent Biotic ability that allows you to control organic enemies and turn them into allies, similar to the Hack ability that controls synthetics. In order to get this ability as a Loyalty mission bonus to use for your character, help Morinth kill Samara during the latter's loyalty mission. However, if you want to keep Samara on your team but still have Morinth's Dominate ability, use the following trick. Play Samara's loyalty mission up to the point where Samara confronts Moritnth. Save the game right before the confrontation. When it is time to select who you will eliminate, choose the option that lets Morinth get the upper-hand on Samara and kill her. Create a separate saved game file. Go to the ship and talk to Morinth. Load the previous saved game then have Samara kill Morinth. You now get to keep Samara as a squad mate and have Morinth's Dominate ability when you choose a bonus loyalty power to add to your character in the prototype upgrade screen.