DALLAS — There’s a marked difference between the first and second acts of Bruce Norris’ Clybourne Park, and it’s not just the 50 years between the acts’ settings, 1959 and 2009. Well, it is, but more about the changes in the way we interact and address a topic as tough as race than it is the differences in fashion and way of life and the inevitable escalation of technology.The play, which opened Friday at Dallas Theater Center and is directed by Joel Ferrell, is what Norris cleverly imagines happened on the other side of the story in Lorraine Hansberry’s groundbreaking A Raisin in the Sun. In one of DTC artistic director Kevin Moriarty’s boldest programming moves since he has been here, both of these shows are running in rotating repertory. ( Raisin is directed by Jubilee Theatre’s Tre Garrett in a brilliant production.) In the first act, we meet the white family moving out of the house that the Youngers of Raisin will move into: Russ (Chamblee Ferguson) and Bev (Sally Nystuen Vahle), who are selling because of a tragedy that happened there. Things heat up when Karl (Steven Michael Walters), the only crossover character from Raisin, arrives to explain what happened with his visit to the Youngers. He has his pregnant, deaf wife, Betsy (Allison Pistorius), in tow. Russ and Bev’s black housekeeper Francine (Tiffany Hobbs, who plays Beneatha in Raisin), her husband, Albert (Hassan El-Amin), and priest Jim (Jacob Stewart) all become involved in an uncomfortable conversation about race.In the second act, 50 years later, the Clybourne Park neighborhood has changed for the worse and is going through gentrification. Young married couple Steve (Walters) and Lindsey (Pistorious) plan to have the house torn down and a new home built there. But the homeowners association has stepped in, and we have a meeting between this couple, HOA members Kathy (Vahle) and Tom (Jacob Stewart), and couple Lena and Kevin (Hobbs and El-Amin), who have petitioned to keep the home standing, as it was the first in that neighborhood to be owned by a black family.There are lines drawn between the characters of the first two acts, and even to the characters in Hansberry’s play (Lena is the great-niece of that play’s Lena). And aside from race, there are similar threads of dialogue, such as world geography. But where the first act tackles big themes, such as the atrocities of war and grieving and black/white race relations, even in a non-Southern city like Chicago, the second act devolves into name-calling, joke-telling and allegations of the R-word.And sadly, it’s just like you’d see in 2009, in a post-PC America in which technology like cellphones, email and social media hasn’t done much for manners, trust or civility. One character sums it up when she says that one joke is “disgusting and juvenile and traffics in the worst possible type of obsolete … stereotypes.”Norris’ play was written before the Trayvon Martin incident and premiered during the first term of our first black president, and its appearance at this point in history makes it all the more topical. It has the marks of an important work because its themes, and the way it addresses them, are going to be relevant for a long time.The cast here is, as in the production of Raisin, first-rate. Walters and Vahle do particularly great work as quite different characters in each act. Walters’ angry Karl turns into a guy who is proud of his honesty in saying what everyone is thinking. Vahle’s not-so-clueless homemaker in the first section is terrific.Once again, the design team, including Bob Lavallee (scenic), Karen Perry (costumes), John Flores (sound) and Valerie Gladstone (wigs/hair), do spot-on work.There is one questionable decision from director Ferrell, though, in that he has the entrance of a character we first see at the very end happening slightly later than Norris wrote it. In the play, it adds deeper commentary on how we’re haunted by ghosts from the past, as this device would act as more of a deus ex machina, interacting with more characters.Norris’ second act is decidedly less sweeping than his first, but you can’t help but wonder if that’s intentional. It reflects how the conversation about race in this country has changed, and not necessarily for the better. In many ways it has devolved in disgusting and juvenile ways.At all costs, catch both of these productions; there will be a few chances in the next two weekends to see them both in one day.