Why do you interpret these figures as racism and sexism?
If only 13% of the American population is black, then any amount higher than that in our prison system constitutes a disproportionate amount of blacks being imprisoned. Since blacks are just like the rest of us except for the color of their skin, that makes this racism.
The OP is probably liberal (like I am), and thus based this thread on the premise that sexism and racism are wrong -- and they are to us liberals. Being a liberal means approaching the question of "how does society get along" with the answer of "tolerance"; we don't exclude those who aren't like us, but instead try to simply live with the differences and try to treat others as equals.
But half of the population doesn't see things the way we do. Being a conservative means approaching societal problems with "exclusion"; if somebody's differences are creating a problem, then prevent them from joining your group. While it strikes me as silly to see skin color as a problem, it is for some people and thus conservatives try to separate from them, even if it means imprisoning them. And unfortunately sexism is an even tougher problem to solve in this regard, as the opposite sex can't be too far removed from oneself, but it is as much as possible (say, by desiring them to stay at home while you work or vice-versa). While this is a valid approach to the problem of a peaceful society, liberals like myself can't live that way... I really don't want to exist in an echo chamber. Perhaps the fact that I'm an atheist posting on a Christian forum will support that assertion.
I'm glad that liberals made "sexism" and "racism" into dirty words so that conservatives feel that they need to distance themselves from those ideas, but it really is a conservative problem. If you are a conservative and thinking of rebutting my argument to pointing out how racist we liberals were by attacking the straw-man of historical Democrats (a party I've never belonged to and would never), you owe it to yourself to read up about the "Southern Strategy"
Southern strategy - Wikipedia which describes the difference between
modern Democrats and Republicans.