What is the production code of the episode directed by Michael McDonald?
CREATE TABLE "table1_25548505_1" (
  "series_num" real,
  "season_num" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" real,
  "u_s_viewers_millions" text
);
SELECT "production_code" FROM "table1_25548505_1" WHERE "directed_by"='Michael McDonald';