This is a good question, as both books show discrimination and the negative effects of it.
In To Kill a Mockingbird, we see great racism in the trial of Tom Robinson. Tom is a black man, and he is accused of raping a white woman, Mayella Ewell. In court, Atticus brilliantly shows that Tom could not have raped Mayella, but a white jury does not see it. Their racism blinds them. Atticus, at one point, calls it a disease. He says:
You know what’s going to happen as well as I do, Jack, and I hope and pray I can get Jem and Scout through it without bitterness, and most of all, without catching Maycomb’s usual disease.
The outcome is the eventual death of Tom Robinson, an innocent man.
In Of Mice and Men, we see discrimination on several levels. First, we see the discrimination of Crooks, a black man. We are not even given his real name. He is called Crooks, because a horse kicked him and now he has a crooked back. Moreover, as the story unfolds, it comes to light that no one has ever visited him on the ranch. He, therefore, lives a completely alienated life.
We also see discrimination against Lennie, someone who is mentally challenged. When Lennie accidentally kills Curley's wife, George knows that there is no place for someone like Lennie. So, he does what he has to do and takes Lennie's life.