This is a long story, but I need some advice, so I’m starting from the beginning. My dad is 100% Ashkenazi Jewish, born and raised in every sense. My mom wasn’t raised Jewish, but it was a well-known family fact that she was legally Jewish because of a fully matrilineal Jewish grandmother from Austria. My parents got married, had me and my siblings, and raised all of us strictly as Jews. We grew up believing we were fully, traditionally Jewish. Recently, for Father’s Day, we decided to buy everyone commercial DNA tests just for fun. My dad’s results came back exactly as expected: 100% Ashkenazi Jewish, with both his Y-chromosome and mitochondrial DNA matching expected profiles. My siblings and I all came back around 65% Jewish, which also made sense. The shock came from our mitochondrial DNA (mtDNA). MtDNA is passed down strictly from mother to mother. Instead of a European or Jewish lineage, all of our tests showed a Native American haplogroup. Overnight, our supposed Austrian-Jewish maternal ancestor simply vanished from our genetic history. I was circumcised, had a bar mitzvah, and went through life with a deeply rooted Jewish upbringing. But according to the science of maternal descent, I apparently am not Jewish. I honestly dont know what to do with this.

I just received your question, and am answering immediately! DNA tests do NOT at all determine one's Jewishness! If your mother's mother was known to be Jewish and the family was raised strictly Jewish (in that generation, intermarriage wasn't so common, and if there was an intermarriage it was usually common knowledge), so you are 100% Jewish irrelevant of what any genetic test shows (they are clearly not 100% accurate), and are irrelevant regarding halachic issues like one's very Jewishness! Don't worry at all, and continue observing as many Jewish mitzvot and traditions as you can! May you have a Shana Tova, Happy and Sweet New Year!