It turns out there’s a very simple explanation why the Castor and Leda clones share the same DNA: They’re both from the same donor.
It was revealed in the penultimate episode of Season 3 of “Orphan Black” that the original Castor donor who Sarah and Co. have been looking for is none other than — drumroll, please — Mrs. S’ own mother, Kendall Malone. It turns out that this whole clone club ordeal is much more “in the family” than previously believed.
After tracking down an ex-murderer who is supposedly the original Castor donor — and who Sarah, Felix and Mrs. S believe to be a man — it’s revealed that Duncan took Kendall’s blood samples while she was in prison. The reason he chose her? She apparently absorbed her twin brother when she was in the womb, which resulted in her having two cell lines, one female and one male. As she puts it, “It’s a helluva twist of nature, isn’t it?”
Of course, this just opens up an entirely different can of worms. Mrs. S was set on killing the Castor donor, but now that they know Kendall is also the Leda donor, they need to keep her alive so they can figure out what’s killing Cosima. It also raises an important question: If Mrs. S is Kendall’s biological daughter, does that mean she also has DNA that could help save the clones?
The season finale of “Orphan Black” airs on Saturday, June 20 at 9 p.m. ET/PT on BBC America.