This unit spans approximately 20 class periods of 40 minutes each. The unit is divided into 8 lessons: The first six lessons focus on Mendelian genetics; the last two lessons touch on molecular genetics.

Previously, students had learned in the Organelles Unit that the function of the nucleus is to house the genetic instructions to build proteins; the last two lessons build on this knowledge.

At the start of the unit, students begin by developing an understanding of inherited and non-inherited traits. Then they develop their initial models, prior to seeing any evidence to explain how traits are inherited. After learning to use pedigrees as evidence, they rule out some of the most common models developed by class members, arriving at an intermediate model that will be revised later--this is the “strong gene” model that says that children inherit traits from the parent with the “stronger gene.”

As the students work with additional sets of evidence presented again as family pedigrees, they develop new models, with most classes developing normative Mendelian models on their own through a series of carefully scaffolded activities. Students then learn the formal method of Punnett Squares; now that they have developed a deep appreciation for the need for a model of inheritance that involves two genetics from each parent, they can readily make sense of Punnett Squares.

The last two lessons integrate students new understanding of Mendelian genetics with their understanding of the function of the nucleus is to house the genetic instructions to build proteins. In the first of these lessons, students use evidence to work out whether there are some humans who are genetically resistant to HIV. In the second lesson, once they have concluded in the previous lesson that some humans are indeed genetically resistant, they use evidence to decide which of two different models better explains the genetic mechanism by which these individuals are resistant. In these lessons, students solidify their understanding of basic ideas of molecular genetics and also gain experience in complex scientific practices of model selection, argumentation, evidence evaluation, and coordinating models with evidence.

NOTE: The genetic unit has as a prerequisite one (not all) of the lessons in the Organelles unit: the lesson on the nucleus.

Download the Genetics Unit (40 MB)