Mew is the genetic source of Mewtwo.
In the Pokémon games, Mewtwo is described as a genetically modified clone created from Mew’s DNA. The result is a powerful Psychic-type Pokémon whose design and abilities reflect an artificial alteration of an ancient Pokémon’s genetic material.
Mew and Mewtwo also have consecutive National Pokédex numbers: Mew is 151 and Mewtwo is 150. That numbering can seem surprising because Mewtwo comes before Mew, but Mew was added late in development and placed after Mewtwo in the index.
The 1998 film Pokémon: The First Movie expanded Mewtwo’s origin into a major story about laboratory experimentation, identity, and the meaning of life. Details vary across games, anime, films, and manga adaptations, but Mew remains the canonical genetic source associated with Mewtwo.