What is the term for a mating between individuals with different alleles at one genetic locus?

The correct term for a mating between individuals with different alleles at one genetic locus is a monohybrid cross. This type of cross specifically examines the inheritance of a single trait, where each parent contributes one of two possible alleles for that locus. For example, if one parent has the genotype Aa and the other has the genotype aa, a monohybrid cross would investigate the resulting offspring's genotypes.

In contrast, a dihybrid cross involves two different loci, focusing on the inheritance of two traits simultaneously. The terms "genotype" and "phenotype" refer to different concepts entirely: genotype describes the genetic constitution of an organism, while phenotype refers to the observable characteristics or traits expressed by that organism.