What is a cross between individuals that possess different alleles for the same gene called?

The correct term for a cross between individuals that possess different alleles for the same gene is "monohybrid." In genetics, a monohybrid cross specifically examines the inheritance of a single trait, where two parents with contrasting traits (i.e., different alleles for the same gene) are crossed. For example, if one parent has a genotype for flower color that is homozygous for purple (PP), and the other parent is homozygous for white (pp), the resulting offspring are hybrids (Pp) for that trait.

In contrast, a dihybrid cross involves individuals that differ in two traits, focusing on the inheritance patterns of two separate genes. A test cross typically involves crossing an individual with a dominant phenotype but an unknown genotype with a homozygous recessive individual, which helps determine the genotype of the dominant parent. Lastly, a back cross involves crossing a hybrid organism back with one of its parents or an individual genetically similar to its parent.

These distinctions clarify why a monohybrid cross is the accurate choice for this situation.