Kate Walsh, Patrick Dempsey Kate Walsh, Patrick Dempsey

Ever wonder how Meredith Grey would have turned out had her mom, Ellis, never developed Alzheimer's and died? Or if Derek had chosen Addison over Mer? Grey's Anatomy executive producer Shonda Rhimes sure did and is answering these questions in the ABC drama's February 2 episode.

"The whole concept is really cool — a Sliding Doors kind of thing," says Private Practice star Kate Walsh, who guest stars. "It's interesting to see all of the characters turned upside down a little. Ellis is alive and well and has changed everything. She has a different relationship with her daughter, which makes Meredith a different person — not the kind of woman who would continue on with someone who's married." Meow!

To create an alternate-universe look, the makeup, wardrobe and hairstylists returned Kate to the way she looked in 2005. "It was really fun for me to be back in the really coiffed hair and red lips," she says. "And all the guys are wearing ties and buttoned-up white coats. Patrick [Dempsey] looked a little like a mad scientist so we were calling him McDreary instead of McDreamy. It was all very strange, creepy and cool."

While the hospital staff perceives the Drs. Shepherd as the perfect couple, Kate says viewers will "see what's really transpiring. There may or may not be a baby on the way."

This may also be the year when Addison becomes a mommy on Private Practice. Kate teases, "She's going to Palm Springs with Jake." Hmmm... perhaps to conceive a baby in the desert? "That's all I'm tellin' ya!"

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