Final answer:
An organism's physical appearance is its phenotype. The genetic makeup of an organism is called its genotype.
Step-by-step explanation:
The observable traits expressed by an organism are referred to as its phenotype. The organism's underlying genetic makeup, i.e., the combination of alleles, is called its genotype. When diploid organisms carry the same alleles for a given trait, they are said to be homozygous for the genotype; when they carry different alleles, they are said to be heterozygous.