Answer: Individual I-1 is heterozygous, genotype Aa.
Very quick reasoning recap (so you can repeat it in exams):
1. Attached earlobes are autosomal recessive, so affected (shaded) people
must be aa.
2. Individual II-2 is shaded, so II-2 = aa.
3. II-2’s parents are I-1 (unshaded) and I-2 (shaded). A child who is aa must get
one a from each parent.
4. I-2 is shaded, so I-2 = aa, and definitely contributes an a.
5. I-1 is unshaded (not affected), so cannot be aa, but must have given an a.
Therefore I-1 must be Aa (a carrier).
6. If I-1 were AA, then all children with aa partner (I-2) would
be Aa and none would be affected, which contradicts II-2 being affected.
So the final genotype of individual I-1 is:
0
