The purpose of this study was to analyze seven widely used high school biology textbooks in order to assess the nature of science knowledge (NOS) and scientific inquiry (SI) aspects they, explicitly or implicitly, conveyed in the Mendelian genetics sections. Textbook excerpts that directly and/or fully matched our statements about NOS and SI were labeled as explicit and excerpts that partially and/or indirectly matched our statements about NOS and SI were labeled as implicit. There was a running count of each NOS and SI aspect that was identified in the textbooks and the instances were noted to be either implicit or explicit. There were 365 instances of NOS and SI aspects counted in 140 textbook excerpts. Of the 365 instances, 237 (65%) were NOS aspects and 128 (35%) were SI aspects. The analysis also revealed far more implicit than explicit instances of NOS and SI. Of the 365 instances, 362 (99%) were implicit and three (1.0%) were explicit. The three explicit instances were all SI aspects. In conclusion, the Mendelian genetics sections demonstrated a multitude of opportunities to teach NOS and SI explicitly, although what was included in textbooks was virtually all implicit. This study demonstrates the importance and value for science educators to examine how teachers use instances of NOS and SI in textbooks. Understanding how teachers use instances of NOS and SI would provide information that could be immediately implemented into professional development programs. Lastly, this research would provide textbook developers with compelling information to update the supplemental instruction materials provided to teachers.