What term describes a genotype in which the two alleles for the characteristic are different?

The term that describes a genotype in which the two alleles for a characteristic are different is heterozygous. In genetics, an organism's genotype consists of the alleles it possesses for a particular gene. When these alleles are not identical, or one allele is different from the other, the genotype is referred to as heterozygous.

For example, if we consider a trait influenced by a pair of alleles, such as flower color, a plant with one allele for red flowers and another for white flowers would be heterozygous for that trait. This contrasts with homozygous, where both alleles would be the same, such as having two alleles for red flowers.

The other terms listed do have important roles in genetics but are not relevant to the specific question about the difference between alleles. Dominant and recessive refer to the behavior of these alleles in terms of their phenotypic expression, but they do not indicate whether the alleles are the same or different.