Parthenogenesis: Virgin Births in Birds

On my birthday comes an interesting article about virgin births being more common than we thought. I knew that parthenogenesis (“virgin birth”) was common in aphids, lizards, and fish, but apparently in birds too. The Atlantic reports:

“In species where parthenogenesis has been extensively studied, the process begins not long after the egg itself is created. When a cell divides in two to make an egg cell, the other half becomes a polar body, which contains a near-identical copy of DNA. Normally, the polar body disintegrates. But studies of other birds have revealed that on occasion, the polar body somehow merges again with the egg, acting like sperm fertilizing it. Because of birds’ chromosome system—ZZ makes males and ZW makes females—all avian parthenotes are males. If an egg with a W chromosome merges with its polar body, the resulting WW embryo will not be viable. Only the ZZ parthenotes ever hatch. But that doesn’t explain why some females go through parthenogenesis but not others.”

There was a good Regenesis episode dealing with a parthenogenesis in a teen girl whom the Norbac scientists initially thought was raped by her father. You can watch it on amazon prime, Regenesis: Season 3. It’s episode 10, “Unbearable”. Wes is part of the Norbac team and also the uncle of the girl (Molly) who is pregnant. He thinks that his brother Eliot (Molly’s father) raped her, and wants his colleagues to prove it with all the DNA testing so he can call the police. The relevant part goes from 34:50-40:47:

Wes: “Did Eliot get Molly pregnant? I want to know, I want to call the police.”

David: “What’s the name of Eliot’s ex-wife?”

Wes: “Andrea.”

David: “Molly got 50% of her DNA from Eliot, and 50% of her DNA from Andrea. The baby got 50% of her DNA from Molly, which breaks down to 25% from her grandmother, and 25% from her grandfather. And she got 50% of her DNA from whoever the father was. Now if Eliot is the baby’s father, that means that 50% of the baby’s DNA comes from Eliot as its father, and 25% of its DNA comes from Eliot as its grandfather, for a total of 75%.

Maiko: “No, but that’s the thing. We checked, and it’s only 50% of Eliot’s DNA in that baby, not 75%.”

David: “Well… then Andrea fucked the milkman. The only way this is possible is if Eliot is only the biological father of the baby, not the biological father of Molly. Call the police, Wes.”

Carlos: “No, but wait a minute, David. We have DNA profiles of Eliot and Molly. And with 100% certainty, Eliot is Molly’s biological father. We keep going in circles.”

David: “Well… then shit.”

Then David examines the DNA analyses of Molly’s baby and finds that it is 100% identical to that of Molly — a clone, an identical twin, a genetic copy, whatever you want to call it. So Eliot is not the father of the baby, because the baby doesn’t have a father. David speculates: “In other for parthenogenesis to occur, Molly’s egg needed to gain an extra copy of DNA somehow. Fertilized without the fertilizer. And then the hard part: that egg DNA somehow had to come alive. Normally it’s the sperm that does that. So we need to look for something that could trigger all of this. My guess is a bacterium. A bacterium that somehow infected her developing eggs.”

Fun science fiction, and not wildly impossible. Scientists say that human virgin births are technically possible though very unlikely.