‘The Big Bang Theory’ finale closes with a big dose of heart

(CNN)The following contains spoilers about “The Big Bang Theory” series finale. As it turned out, though, the episode (rather sweetly credited to a dozen writers, including co-creators Chuck Lorre and Bill Prady) served as a conduit to showcase the way in which the show itself has changed — adding key female characters, marrying off the guys and graduating to more grown-up problems and issues, without giving up their passion for things like comic books and “Star Wars” movies. The graduation to adulthood saw the characters take another major step in the finale, as Leonard (Johnny Galecki) and Penny (Kaley Cuoco) learned that they were pregnant — joining Howard (Simon Helberg) and Bernadette (Melissa Rauch) in the parents club — a …