"Janet's Mystery Gene" is the twelfth episode of the second season of The Magic School Bus Rides Again.
Carlos is assigned to read to the kindergarten class with, to his chagrin, Janet, who wishes to regail the kids with a telling of her autobiography.
Arnold reveals that Janet, like him, is overly nervous but hides it with an arrogant front. After he states that it runs in the family, Ms. Frizzle proposes a field trip into Janet's DNA to look for her "nervous" gene.
Turning the bus into a DNA Scanner, the CRISPR Express, Ms. Frizzle and the class run along Janet's code, finding segments that determine her hair color, shape of her ears and her in-grown toenail.
Impatient, Carlos speeds up the bus, causing damage to Janet's DNA. The DNA recombines itself but causes physical changes to Janet, first her hair color from red to black, then her nose and ears, and ultimately what kind of species she is: a plant, cat, penguin, a komodo dragon- all because
To repair her DNA, the class samples Arnold's hair and uses its DNA as a template to fix Janet. They manage to repair her but end up giving her freckles, which turns out to be a dominant genetic trait. After discovering why and repairing the mistake they return ot the bus and watch the outcome. Her freckles are gone, but somehow, Janet ends up with a deep male voice. They have to start over. Just as Janet enters the kindergarten classroom, transforms into a monkey, which the kids cheer in excitement at. Eventually, they completely restore Janet's code, normal voice and clear skin in all.
Carlos abandons the search for Janet's nervous gene and returns to stop Janet from reading her autobigraphy. Janet scolds him for being late and Carlos confesses about the mission to find her nervous gene and replace it with a nice gene, which leaves Janet non-plussed. She scoffs at Carlos, stating that a nervous gene is nonsense and that she didn't get nervous until a certain embarrassing point in her life. Carlos realizes that Janet's nervousness was simply a culmination of her experiences. Instead of her autobiography, Janet adlibs a story about Carlos, but to Carlos and the class' surprise, she manages to be nice to the kids.
Ultimately, the kids loved Janet and she is seen being chased by them, wanting to hug her. Nervous as she is, she runs from them.
Prof. Frizzle's Segment
The caller asks if it is really possible to change a person's genes to change the way they look. Prof. Frizzle says no but states that scientists are working on editing genes for preventing genetic diseases and, in the future, eradicating other genetic abnormalities.
Is there a nervous gene? Prof. Frizzle states that, like siblings living in different countries and learning different languages, a person's attitude and personality is not dependant on their genes but comes from their experiences. Janet and Arnold, for instance, were both raised by their parents to live safely and cautiously.
- Janet's freckles are removed in this episode as a plot point, but they appear again briefly at 7:04 before Ms. Frizzle and the class begin making changes to her DNA.
- Janet was implied not to have freckles in this episode, but in all her appearances in Season 5, she did have freckles.
- Janet turning into an aardvark wearing glasses and carrying a book is a possible reference to Arthur Read from Arthur.