What type of cross involves individuals that are homozygous for different alleles?

A monohybrid cross is specifically characterized by the mating of two individuals that are homozygous for different alleles of a single gene. For example, if one parent is homozygous for the dominant allele (AA) and the other parent is homozygous for the recessive allele (aa), the resulting offspring will all be heterozygous (Aa). This type of cross is used to observe how a single trait is inherited and allows for the prediction of ratios of genotype and phenotype in the offspring.

In the context of the other options, a dihybrid cross involves individuals that are homozygous for different alleles of two genes, which is more complex than a monohybrid cross. A test cross usually involves crossing an individual of unknown genotype with a homozygous recessive individual to determine the genotype of the former. A back cross involves mating a hybrid organism back to one of its parents to reinforce certain traits, but it is not limited to individuals who are purely homozygous. Thus, the highest clarity in terms of homozygosity for different alleles is found in a monohybrid cross.