The original script called for McKay to reveal that he had a brother on Earth, not a sister. David Hewlett asked the producers if the sibling could be a sister instead because he has a sister who is an actress. He didn't necessarily ask that she be cast in that role but he wanted to leave open the possibility for a future episode. The producers agreed and Kate Hewlett was indeed cast as Rodney's sister in the Season 3 episode "McKay and Mrs. Miller."