This is one of 25 assessment probes from the book,” Uncovering Student Ideas in Life Science, Volume 2: 25 New Formative Assessment Probes”, by Page Keeley. All assessment probes in this collection are aligned to a particular science concept and field-tested by several teachers in classes of diverse student backgrounds. Assessment probes consist of the actual one-page probe for use with students, and a section of several pages with teacher notes. Teacher notes include information on the purpose of the probe, related science concepts, an explanation of all answer choices, curricular and instructional considerations, suggestions for administering the probe, related standards (National Science Education Standards, 1996), related ideas in Benchmarks for Science Literacy (AAAS, 1993), related research, description of common student misconceptions, suggestions for instruction and assessment, and related NSTA science store publications and journal articles. An assessment probe is a purposefully designed, multi-grade level question that asks students to provide a two-part response. Part one consists of a selected response, and part two asks students to provide an explanation. This format helps teachers identify students’ existing ideas about phenomena or concepts, which can help inform the design of instruction. Assessment probes can also be used to engage students, encourage thinking, and promote sharing of ideas. When implementing probes in the classroom, the authors suggest using the probe to encourage teacher-student, student-teacher, and student-student feedback on learning. The “Baby Mice” probe elicits students’ ideas about the inheritance of genetic traits. The probe describes a scenario in which five black mice and two white mice resulted from the mating of a black male and a white female. The probe provides explanations about the phenotypes of the offspring from seven friends. Students are asked to select which friend they agree with the most and to explain their thinking. The probe can be used before instruction to elicit prior knowledge and identify students’ misconceptions. This information can be useful in planning instruction and determining students’ prior knowledge.