Second, we’re talking about ethnicity here, not religion. Jews are also an ethnic group. Y-DNA is very relevant.
Ethnicity is not what was being talked about just now; You were talking about DNA lineage.
Ethnicity deals with cultural self-identity, which includes religion and does not deal at all with DNA relation.
My understanding, though, is that Jewish culture actually has a long history of genealogy via family tree mapping long before DNA testing was available. That does have some ethnic connection as a cultural tradition.
Ethnicity is not what was being talked about just now; You were talking about DNA lineage.
Ethnicity deals with cultural self-identity, which includes religion and does not deal at all with DNA relation.
My understanding, though, is that Jewish culture actually has a long history of genealogy via family tree mapping long before DNA testing was available. That does have some ethnic connection as a cultural tradition.