Polygenic is a Mixed Origin subtype. Specifically, it means a multiple origin plural, especially if those multiple origins cause the plural to have a lot of members.
Some examples of reasons people might use Polygenic:
- In place of Pangenic, meaning "probably all origins, but since the system doesn't know every origin, they can't say that."
- A way to say the origins mixing together made you Polyplural in some way.
There can be other reasons why someone would prefer Polygenic over other, similar Mixed Origin types.