<Tr> <Td_colspan="7"> When Izzie's daughter, Hannah Klein, is brought to the hospital for leukemia treatment, her adoptive parents come searching for Izzie, and ask her to donate her bone marrow in support . She is saddened to learn that her daughter does not want to see her, but is surprised to see how alike they are . George helps Izzie out, but forgets about a coffee break with Callie . Mark offers to be Webber's wingman, to get him back into dating . Derek comes to the conclusion that his relationship with Meredith is the only thing standing in his way to become the Chief of Surgery . Colin continues to intrude on Burke and Cristina's lives with an impending surgery he will perform . He tries to convince Cristina to break up with Burke, due to their targets being completely different . After realizing that Cristina has changed, Colin drops out of the race for Chief and leaves the hospital . Meredith starts to grow closer to her stepmother, Susan, but they experience a blip when Meredith snaps at her for her constant mothering . A couple arrives at Seattle Grace Hospital to see Ava, whom they initially believe to be their daughter, but the mother rejects Ava without telling her . They leave Alex to inform Ava, causing Ava to lash out . </Td> </Tr> <Tr> <Th> 57 </Th> <Td> 21 </Td> <Td> "Desire" </Td> <Td> Tom Verica </Td> <Td> Mark Wilding </Td> <Td> April 26, 2007 (2007 - 04 - 26) </Td> <Td> 20.08 </Td> </Tr> <Tr> <Td_colspan="7"> The interns of Seattle Grace Hospital start to use every free minute to study for their upcoming exam which will determine their entire residency in the surgical field . Cristina is jealous of George who can study with Callie, whose learning cards have become legendary . After the realization that George and Izzie might have feelings for each other, Callie decides to give the cards to Cristina . The attending physicians vie for the Chief position by tending to the chairman of the hospital board, after he is admitted as a patient . They soon learn that there is a fish in his urinary tract and learn that his wife has been aware of his affair with his secretary . She eventually resigns and leaves him, and his wife asks for divorce . In the clinic, Izzie treats a patient with a recurring cold, which turns out to be a symptom of something worse . Webber starts to question his decision to retire as he believes that there is a lot more he can do as a surgeon and cannot be done with his career in his early fifties . Cristina gets annoyed at Burke as he tries pressuring her into choosing a flavor for their wedding cake while she is trying to study . Addison and Alex deliver Ava's baby, through a cesarian - section, before sleeping together, but afterwards Alex tells her to make sure that it never happens again . Derek starts to question his relationship with Meredith, feeling that he is the only one putting an effort for it to work out . George tells Izzie that he is considering transferring to a different hospital . </Td> </Tr> <Tr> <Th> 58 59 </Th> <Td> 22 23 </Td> <Td> "The Other Side of This Life" </Td> <Td> Michael Grossman </Td> <Td> Shonda Rhimes </Td> <Td> May 3, 2007 (2007 - 05 - 03) </Td> <Td> 21.23 </Td> </Tr>

Who becomes chief of surgery after webber season 3