Based off of the hit television show NUMB3RS, this lesson shows students the scientific reasoning behind the societal taboo of incest. Students complete a Punnett square to determine the chances of an offspring inheriting two recessive alleles from the parents, in which case the parents have the same father. Students see that the probability of genetic defect is higher in inbred pairings than in the general population. Students conclude the lesson by running a simulation and making observations of the results.