ALIENATION AND DISCRIMINATION
Crooks is the main person who is discriminated against. This is due to the fact that he's black. Nobody listens to anything he says, "If I say anythin', it's just a nigger sayin' it." Another reason he's not as accepted is because he's got a crooked spine, so he works in the stable, away from the other workers.
Crooks likes his privacy. He's not welcome and doesn't intrude on the other workers, and he expects the same rights. Slim's usually the only person who visits him, until Lennie comes into his room. This is when Crooks first hears about the dream. Candy and Lennie talk to him about it, and he becomes very interested. He offers to do jobs for them when they get the place, but when Curley's Wife comes in and treats him badly, he tells Candy he was only joking about being a part of their dream, since his pride has been cut down and he believes that he's not "equal".
Crooks had been discriminated against and isolated for most of his life. When he was a little boy, he used to play with white kids, because there was no other black family around that area. His father didn't like him playing with the white kids, because he'd been discriminated against by whites, and he knew that one day Crooks would be as well.
Curley's wife is alone on the ranch while the other guys are working, because she's a woman. Her alienation is dramatically increased by the fact that she's a tart. Curley doesn't actually love her, he just treats her as a sexual trophy. She got told that he could have been an actress, and been in movies, but her mother wouldn't let her, so she runs away from...