Final answer:
A genotype with two different alleles, like Yy, is known as heterozygous. It indicates the presence of one dominant and one recessive allele. Codominance is a different pattern where both alleles are equally expressed.
Step-by-step explanation:
When a genotype has two different alleles at a locus, such as Yy, the correct term for this is heterozygous. This term implies that one allele is dominant (represented by the uppercase letter, Y) and the other is recessive (represented by the lowercase letter, y). Genotypes can alternatively be homozygous dominant (YY) or homozygous recessive (yy) which means they have either two copies of the dominant allele or two copies of the recessive allele, respectively. In comparison, codominance is a situation where both alleles are equally expressed in the phenotype, as observed in certain human blood types where multiple alleles exist at the population level. This diverse genetic expression is foundational to the study of inheritance patterns in organisms.