AND CO-STARRING AS ZAC EFRON'S MOM, MARY-KATE OLSEN!

Last night I was watching a new (for South America's Sony Channel) episode of Grey's Anatomy, and my wandering mind settled on something intriguing and slightly disconcerting. It involved guest star Tyne Daly (above), Tony winner and Emmy winner for Cagney & Lacy, Christy and Judging Amy. It had nothing to do with her performance, which was as bold and blustery as usual. It was the role she was playing: Dr. McDreamy's mom.

Nothing too peculiar there, right? After all, at 63, the actress is certainly old enough to play the mother of Patrick Dempsey, 43, and when it comes to the ages of Anatomy's cast and the characters they play, watching requires a slight suspension of disbelief. But once I started to play Six Degrees of Separation in my head, the creeps started to settle in. Dr. McDreamy is the ex-husband of Dr. Addison Montgomery, now the central character of the Anatomy spin-off, Private Practice. In early Practice episodes, Addison was dancing around in the romantic orbit of Peter Wilder, played by Tim Daly, Tyne's brother, who recently was involved in a romantic story arc with Violet Turner, played by Amy Brenneman, who called Tyne "mom" for six seasons on Judging Amy.

Got all that?

Alright. Now, what's wrong with this picture? Basically, the casting directors are saying that Tyne could potentially play the mother of her real-life brother, who, at 53, is 10 years her junior. True, Tim Daly is a hunky, youthful 53, and Tyne has the matronly, overbearing mom thing down, but come on. As an actress, Tyne -- who, by the way, I think looks great -- always has been refreshingly vanity-free (she even allows her hair to go naturally gray, a rarity in Hollywood), but what an ego boost!

Consider a similarly age-gapped brother and sister duo, Eric, 53, and Julia Roberts, 41. Would any casting director even consider hiring Eric (who was born in the same year, 1956, as Tim Daly) as the Brothers & Sisters love interest of Sally Field, who was born in the same year, 1946, as Tyne Daly, played Julia's mom in Steel Magnolias, and is closer to his age than Julia? Or would they cast him as the father of Jude Law, Julia's love interest in Closer who, at age 36, is chronologically young enough to play his son?

Probably, no. But why not? Actresses seem to almost always get the short end of the casting stick when it comes to playing mothers and lovers? In order to land her greatest screen role, in 1962's The Manchurian Candidate, Angela Lansbury had to play the mother of Laurence Harvey, who was almost exactly three years her junior. Three years earlier, Laurence had been nominated for an Oscar for playing the supposedly much younger lover of Oscar winner Simone Signoret, only seven years older, in Room At The Top. Then there is Unfaithful's Diane Lane, 44, and Oliver Martinez, 43. In that film, he was supposed to be the "younger" man. Compared to whom? Richard Gere? Diane's husband in Unfaithful (and her love interest in two other movies), Gere, at 59, is nearly 20 years older than Diane's real-life husband, Josh Brolin?

Something's rotten in the state of Hollywood. Sure Sean Connery, 78, once played onscreen dad to Dustin Hoffman, 71, but he also got to play the romantic lead opposite Catherine Zeta-Jones, 39, an actress who knows a thing or two about vintage leading men (her husband, Michael Douglas, is 64), in 1999's Entrapment. According to an interview I once read with Angela Bassett, 50, she was up for Catherine's role but didn't get it -- presumably because she was too black, too old or both.

If Jack Nicholson, who turns 72 tomorrow, can win an Oscar for playing the love interest of Helen Hunt, 45, in As Good As It Gets, without the age difference ever being mentioned in the screenplay, why can't Eric Roberts romance Sally Field on Brothers & Sisters? For the steadily employed but under-appreciated actor, it certainly would be nice work if he could get it.