Mew is similar to a vertebrate embryo. It shares many traits with cats. Its morphology is also vaguely similar to a jerboa, having large hind legs and a long skinny tail. It is believed by scientists to be the ancestor of all other Pokémon, a reference to the recapitulation theory.
Meaning, Mew is based off of an embryo and a cat.
Like Mew, Mewtwo has some feline characteristics, but its body structure is much larger as a result of gene splicing. Mewtwo also has some characteristics of a grey alien.
Meaning that Mewtwo is, obviously, based off of a cat (like Mew) and somewhat represents and alien.
Hope this helps!