Which of the Following Genotypes is Heterozygous

Question

Which of the following genotypes is heterozygous?
A) Aa
B) Ab
C) aB
D) ab
E) aa

Accepted Answer

Heterozygous means having two different alleles of a gene. In option A, there are two different alleles (A and a), so it is heterozygous. The other options either have the same allele twice (aa or bb) or have alleles for different genes (Ab and aB).