Episode Synopsis: "Donor Unknown" charts the story of 20-year-old JoEllen Marsh, who was raised by two mothers in Pennsylvania, as she searches for her sperm-donor father, known only as "Donor 150." Thanks to an online registry for the children of sperm donors, she meets half-siblings that she never knew existed; and, thanks to a New York Times article about her quest that he just happens to see in a Venice, Cal., coffee shop, eventually manages to connect with her biological dad.