A genasi comes into being in one of two ways; as the combined offspring of a djinn and a humanoid creature (typically a human, or one with elf or orc blood); or from heavy exposure early on to one of the Elemental Planes. The types of genasi are determined by the djinn or Elemental Plane to which they possess a connection; the Elemental Plane of Air, Earth, Fire, or Water.
On Havilon, genasi are incredibly rare. Rarer even than the aasimar, they have no established home on the new continent, and most genasi will flock to big cities where they more easily can blend in.