Probably the character who challenges racial stereotypes the most in the play is Beneatha. Unlike the stereotypical uneducated African American, Beneatha is going to college and wants to become a doctor. This even challenges her own brother's ideal of what a Black woman should do. Several times during the play he asks her why she doesn't become a nurse like other women?
In addition, Beneatha is not content with the role that was assigned other Black women, women like Mama and Ruth who clean other people's houses or do their laundry. Instead, Beneatha wants to explore different ways of expressing herself, even if it means that Ruth and Mama laugh at her attempts. She even has the audacity to say she doesn't believe in God---a remark she is quickly forced to take back when Mama slaps her. But she is also the character who helps Walter to stand up to Linder and his offer. When Linder says he wants to buy the Youngers out, Beneatha quips, "Thirty pieces of silver" alluding to the price put on Jesus' head.
However, Hansberry also seems to believe that Beneatha still has a lot to learn from the traditional ways--especially those of Mama. When Beneatha wants to disown Walter for losing the money, Mama is quick to ask "When is the time to love a person the most?" and makes Beneatha stay to support her brother as he faces Linder for the second time. Thus, Beneatha seems to represent a new kind of African American, one who is educated, cultured but still can learn from the traditional values that helped African Americans survive in a hostile world.
Hansberry challenges the stereotypes of African Americans in her depiction of Ruth. I think that this is evident when Ruth seriously considers having an abortion. Ruth's decision to have an abortion belies society's perception of African American women of her time.