This instructional activity is adapted from a Connected Mathematics Unit, How Likely is It? This investigation introduces biology as a source of applications for probability. In this instructional activity, Curling your Tongue, students determine how many students in the class can curl their tongues and use this data to make predictions about the probability of any one student being able to curl his or her tongue. Then they "Tracing Traits-the experimental method is compared with the way in which geneticists study a person's traits: by examining the genetic makeup of the person's parents, grandparents, and other relatives. Students then gain experience with determining whether people have the tongue-curling trait based on the genetic probabilities. This lesson plan was created as a result of the Girls Engaged in Math and Science, GEMS Project funded by the Malone Family Foundation.