From the most recent author's note:
The story of HPMOR is built around the parallel-universe versions of those roles, and those roles (with one exception) retain whichever genders they had in canon.
What is the exception?
The exception could conceivably be Blaise Zabini. From the TV tropes article titled "Ambiguous Gender" -
Harry Potter's Blaise Zabini got a single mention in book one, which sparked years of furious debate over his or her gender. Fan Fiction summaries often stated Boy!Blaise or Girl!Blaise, each with their own set of conventions and fanon personalities. (Boy!Blaise was often suave and Italian, Girl!Blaise often red-haired.)
It was not revealed until the sixth book that Blaise was male. While Eliezer chose to keep him male, he likely had the option to chose given the character's very uncertain past.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 93. The previous thread has passed 300 comments.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18,19,20.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: