“Found in the estate papers,” she said. “Turns out Ana wasn’t AB at all. She was O negative her whole life. The AB was a transcription error made decades ago.”
“That’s your lab task,” Dr. Reeves smiled. “Using only the pedigree and a fresh blood sample from Julian, determine if he could be Ana’s son—and whether the estate should accept or reject his claim.” lab activity blood type pedigree mystery
Silence. Then Priya, the group’s quietest member, spoke up. “That changes everything. Two type A parents can have a type O child. But an A and an AB cannot produce a type O child. Ever.” “Found in the estate papers,” she said
“Standard family,” Leo shrugged. “What’s the mystery?” The AB was a transcription error made decades ago
After running the simulations, Maya’s group confirmed that a type O child can only come from a type O parent or a heterozygous A/O or B/O parent. Since Ana was OO, Julian’s father must have contributed an O allele. That means Julian’s biological father was either type O, A, or B—but not AB.
Leo frowned. “But what if the old record is wrong? Blood typing isn’t perfect. Or what if Ana’s type changed? No—that doesn’t happen. Or what if—” He stopped. “Wait. What if Julian knows that? What if he’s counting on us not checking Ana’s historical type?”