Class blood test reveals student's 'dad' actually her uncle

A teenager in the US has reportedly caused her parents to get a divorce after a biology class experiment proved her 'dad' was actually her uncle.

Anya Hettich of California State University said it happened Monday last week during a biology lecture.

"We're discussing blood types and this girl was trying to figure out why her blood type didn't make sense on her Punnett square," the 19-year-old wrote on Twitter. "She told the prof her dad was O and her mom was A, but yet she was AB."

A child needs at least one parent with type B or AB blood in order to have AB blood. Her professor explained to the student it was impossible for her to have AB blood if neither of her parents did.

"My prof told her to talk to her parents to double check the blood types and all and make sure the information was correct," wrote Ms Hettich.

"She comes back to class today and my prof made a point to ask if she was mistaken or confused."

She was neither.

"This girl is ballsy, lemme tell ya. She announces it to the entire class of 243 people. Turns out, her mom had an affair with her husband's brother, which is his step brother. So technically, she's been raised by her uncle and not her dad her entire life - her mom hid it from the both of them for 21 years."

But the truth hasn't brought the family closer together.

"Now they're getting a divorce," wrote Ms Hettich.

After other Twitter users cast doubt on the story, another student pointed out she'd tweeted about the strange day in class a day before Ms Hettich told her version of the story.

Ms Hettich has declined to talk to media about it.