Is that true that Adolf Hitler's mother or maybe one of his female ancestors was Jew?

"There were rumours that Hitler was one-quarter Jewish and that his grandmother, Maria Schicklgruber, became pregnant while working as a servant in a Jewish household. The implications of these rumours were politically explosive for the proponent of a racist ideology. Opponents tried to prove that Hitler had Jewish or Czech ancestors. Although these rumours were never confirmed, for Hitler they were reason enough to conceal his origins."