In humans, the ability to bend the thumb back beyond vertical is called hitchhiker's thumb and is dominant to the inability to do so (OMIM 274200; see Problem 41). Also, the presence of attached earlobes is recessive to unattached earlobes (OMIM 128900).

Using all available and willing members of your family, or members of another family if yours is not easily accessible, trace the transmission of both traits in a pedigree. Use allelic symbols H and h for the thumb and E and e for earlobes, and identify the genotypes for each family member as completely as possible. Bring the pedigree back to share with your group.