It fits in really will with the reproduction unit because they can put their details in, choose a partner, have a baby and see what it looks like. Genetics is complicated but extremely interesting. I have used tongue rolling as an example of how we inherit genes from our parents because it only has two options can or can't. Use a dice or a coin to talk about what we inherit because it really is that random.
This activity is connected to the Reproduction unit. Let the students play around with the simulator. I have put some investigations in the worksheet but they have many solutions, they are just there to guide their inquiries.
Link to activity (pdf): Genetic calculator activity