Reference for Bava Batra 219:1
אלא אי אבוה דאמיה מיוסף אמה דאמיה מיתרו אי אבוה דאמיה מיתרו אמה דאמיה מיוסף דיקא נמי דכתיב מבנות פוטיאל תרתי שמע מינה
But [this is really the explanation], if his mother's father [descended] from Joseph, his mother's mother<span class="x" onmousemove="('comment',' But not his own mother. ');"><sup>1</sup></span> [descended] from Jethro; if his mother's father [descended] from Jethro, his mother's mother [descended] from Joseph.<span class="x" onmousemove="('comment',' In either ease, Phinehas was several generations removed from Jethro, while Jonathan, being the son of Gershom, was only two generations removed. ');"><sup>2</sup></span> [This may] also [be confirmed by] deduction, for it is written, of the daughters of Putiel, from which two<span class="x" onmousemove="('comment',' The Yod in Putiel is regarded as a sign of the plural. ');"><sup>3</sup></span> [lines of ancestry]<span class="x" onmousemove="('comment',' Joseph and Jethro. ');"><sup>4</sup></span>