When a new mutant or robot was made, they were referred to in a class called a generation. A mutant's generation was signified by a number, while a robot's was signified by a letter.
When a certain breed of successful mutants were made, they were given a number.
The earliest known generation
The Director of Itexicon was the only known member of this generation. She was 107 years old and a human-Galapagos tortoise hybrid.
The Erasers were the only known members of this generation. Even though it was an early generation, those who were made as an Eraser were still considered from this generation. The Erasers continued to be produced and experimented on, which eventually led to them having wings. This generation is no longer in existence, though, due to the lost interest in recombinant-DNA life-forms, which led to their "retirement" and replacement by the Flyboys. Ari was considered to be the last of the Erasers to die. However, FANG showed that there were still some Erasers left.
The avian-human hybrids made up this generation. The Flock, as well as a winged girl they rescued from the Institute, belonged to this generation. Unlike the Erasers, this generation wasn't so mass-produced. Many things are unknown about this generation, except that the hybrids would mutate differently over time.
The Gen77 recruits for Fang's Gang (Ratchet, Holden, Kate, and Star) and Beth are the only known members of this generation. Unlike the others, they are not recombinant-DNA life-forms, but have enhanced abilities like strength or speed.
When the Director presented Omega at a mutant showcasing in Saving the World and Other Extreme Sports, she said "Generation Omega", possibly hinting of another generation branch. Omega was the only known member; possible other members are Brain on a Stick.
Many more recombinant-DNA life-forms and enhanced humans were seen at the School, the Institute for Higher Living, Itexicon's headquarters in Germany, and in Africa; however, their generations were never identified.
When a new breed of robots or cyborgs were made, they were given a number.
Generations C through G
These generations were mentioned briefly by the Uber-Director in The Final Warning; he stated that these generations were failures compared to Generation K. It is possible that the Flyboys were somewhere between Generations C and G.
These robots were see in The Final Warning; they were addicted to electric shocks given by the Uber-Director.