Where does “জো” come from?

জো (Bengali) comes from Hindi जो, from Urdu جو, from Sauraseni Prakrit 𑀚𑁄, from Sanskrit यः, from Proto-Indo-Aryan Hyás, from Indo-Iranian *Hyás, from Proto-Indo-European Hyós — who, which; already.

Ancestry of “জো”, step by step

Step	Language	Word	Meaning
1	Hindi	जो	the relative pronoun; if
2	Urdu	جو	the
3	Sauraseni Prakrit	𑀚𑁄	—
4	Sanskrit	यः	—
5	Proto-Indo-Aryan	Hyás	—
6	Indo-Iranian	*Hyás	—
7	Proto-Indo-European	Hyós	who, which; already

Every word from Proto-Indo-European Hyós →Every word from Indo-Iranian *Hyás →Every word from Proto-Indo-Aryan Hyás →