As a class, make a checklist of traits common in students' families.
Life expectancy is a trait that's too difficult to check.
Remind students that not all family members share all genetic traits. They may find differences in eye color, for example. Review dominant and recessive genes and ask students to look for evidence of them in their study. Similarly, if students find matches in environmental traits, discuss how a scientist might prove whether the traits are genetic or not. Yet in some cases of identical twins, only one develops Alzheimer's disease.