The part where Cat sneezes on the microscope was not originally in the script but was a joke done by Danny John-Jules in rehearsal. The crew liked it so much that it was decided to include it in the episode.
Robert Llewellyn stated that some of his young relatives were invited to watch the filming of this episode, but were left unimpressed because the story meant that he spent much of the time not wearing his Kryten outfit, and instead just appeared to be the same "boring Uncle Rob".
Lister's reaction to Kryten's "double Polaroid" was not actually planned: Craig Charles had no idea he'd be seeing the real thing, and was quite startled when he realized what it was.
The script reveals that the title "D.N.A." means "Do Not Alter".
At least six cut dialogue scenes and jokes appear on the Series IV DVD, and with more of the Mutton Vindaloo Beast seen. As it comes at the Robo-Lister, he fires off a number of blasts from the bazookoid which miss the Leopard Lager can in the beast's maw, before finally hitting it and blowing up the beast (therefore more closely mimicking the ending of Jaws (1975)).