'Grey's Anatomy's' Shonda Rhimes, Sara Ramirez Ponder Destiny in 'If/Then'

ABC/VIVIAN ZINK

"Grey's Anatomy's" Sara Ramirez and Kevin McKidd

Grey's Anatomy's "If/Then" alternate universe episode will turn Callie Torres' world -- and the lives of pretty much everyone at Seattle Grace -- on its head when Meredith begins to ponder what life would have been like had her mother not had Alzehimer's.

our editor recommends

'Grey's Anatomy' Enlists Summer Glau

'Grey's Anatomy's' Kim Raver on Handling Tragedy: Teddy Will Be Different Than Izzie

"As things start to unfold, we in the writers' room kept coming up with more and more things if Meredith had been a shiny, happy person," Grey's creator Shonda Rhimes tells The Hollywood Reporter, noting that Derek would have remained unhappily married to Addison (Kate Walsh).

Meredith's (Ellen Pompeo) peppy persona -- she winds up engaged to Alex! (Justin Chambers) -- also creates a ripple effect for those around her, with the openly gay Callie (Sara Ramirez), having never met Erica Hahn (Brooke Smith), instead married to Owen (Kevin McKidd).

STORY: 'Grey's Anatomy': Kate Walsh, Kate Burton Returning for February Episode

"They're two people who have no business being together," Rhimes says. "He's pining for somebody else [and] she's having all these unexplained feelings for Arizona because [Callie] is the heart surgeon so she never had her first experience with a woman."

While Ramirez tells THR that the duo winds up married with children -- something Cristina is dead-set against -- she notes that the hour really is about not really being able to change your destiny, no matter what decisions you make.

"There are certain things that will find you in this journey of life no matter what choices you make, no matter what road you go down," Ramirez says of whether Callie will find her way to Arizona (Jessica Capshaw) and "see the leaves." "Sometimes it won't make that much of a difference because your destiny will find you no matter what."

STORY: 'Grey's Anatomy's' Shonda Rhimes: Big Explosion Ahead for Cristina and Owen

Callie, who in the alt universe is a cardio surgeon, will juggle her personal life (describing Owen as a "great father") with a demanding career under the mentorship of chief Ellis Grey (Kate Burton), who runs a tight ship but has taken an interest to her and heavily influenced Callie's choices. Ramirez notes Callie's place in the Seattle Grace hierarchy -- and relationship with Ellis -- will create a different dynamic for between Callie, Cristina and Meredith, who views her as someone she could learn from.

"Ellis is very much pushing her daughter to be better and you'll see Meredith dealing with that kind of mother," she says. "Callie is in a really good position at the hospital and she's well-respected in her field and is in a position that Meredith wants to be in good standing with."

STORY: 'Grey's Anatomy's' Kevin McKidd: Owen and Cristina Have 'Brushed A Lot Under the Carpet'

Meanwhile, Ramirez teases that Cristina (Sandra Oh) is "just a runt for Callie" and while she's respected, Callie has surpassed her to be an amazing cardio surgeon and attending.

"She has no real interest in her other than her abilities," she says. "If she can save a life, great, get her in my OR, but other than that, Callie doesn't really get her."

Watch a promo for the "If/Then" episode below. Do you think Arizona is Callie's destiny? Grey's Anatomy returns Thursday, Feb. 2 at 9 p.m. on ABC.

Email: Lesley.Goldberg@thr.com; Twitter: @Snoodit