Sanhedrin 58B

אביו דומיא דאמו, ואמו דומיא דאביו. לא משכחת לה אלא באחווה.

that the term “his father” should be interpreted in a way that is similar to the term “his mother,” and “his mother” should be interpreted in a way that is similar to “his father.” You find such an interpretation only with regard to sisterhood, i.e., “his father” is referring to his father’s sister, and “his mother” is referring to his mother’s sister.

ורבי עקיבא: מוטב לאוקמיה באשת אביו, דאיקרי ״ערות אביו״, לאפוקי אחות אביו, ד״שאר אביו״ איקרי, ״ערות אביו״ לא איקרי.

And R' Akiva holds that it is preferable to interpret the term “his father” as referring to his father’s wife, who is referred to as his father’s nakedness in the verse: “You should not uncover the nakedness of your father’s wife; it is your father’s nakedness” (Leviticus 18:8), to the exclusion of his father’s sister, who is referred to as his father’s kin in the verse: “You should not uncover the nakedness of your father’s sister; she is your father’s kin” (Leviticus 18:12), and who is not referred to as his father’s nakedness.

תא שמע: ״ויקח עמרם את יוכבד דדתו״. מאי לאו, דודתו מן האם?

Come and hear a proof for the opinion of R' Akiva from the verse: “And Amram took Jochebed his aunt as a wife” (Exodus 6:20). What, was she not his maternal aunt? Presumably, Jochebed was the sister of Kohath, Amram’s father, from both of Kohath’s parents, and not from his father alone. Evidently, a descendant of Noah may marry his father’s sister.

לא, דודתו מן האב.

The Talmud rejects this proof: No, she was his paternal aunt, Kohath’s half sister. Since she was not Kohath’s sister from his mother’s side, she was not forbidden to Amram.

תא שמע: ״וגם אמנה אחתי בת אבי היא אך לא בת אמי״⁠ – מכלל דבת האם אסורה.

Come and hear a proof for the opinion of R' Eliezer from what Abraham said to Abimelech with regard to Sarah: “And moreover, she is my sister, the daughter of my father, but not the daughter of my mother; and so she became my wife” (Genesis 20:12). By inference, the daughter of the mother of a descendant of Noah is forbidden to him.