Most students have heard about situations in which the paternity of a child is questioned; in a surprising reversal, in this case study, maternity is in question. Designed for an introductory biology course, the case involves concepts from genetics, inheritance, and the formation of pedigrees. Students develop hypotheses to explain how a mother might not be genetically related to two of her three sons, then reject these and form new hypotheses as additional data are revealed in a progressive-disclosure format. (Contains 3 figures.)