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The term that describes the genetic makeup of an organism is genotype. The genotype refers specifically to the set of genes an organism carries, which can include various alleles for specific traits. It provides the underlying genetic information that can influence an organism’s characteristics but is distinct from phenotype, which is the observable expression of those genes.

Genotype plays a crucial role in understanding inheritance patterns and the potential for variation within populations, as it encompasses both dominant and recessive alleles. For example, in a plant, the genotype could determine whether it has purple or white flowers based on the alleles present.

The other terms provided have different meanings. Phenotype refers to the observable traits and characteristics of an organism resulting from the interaction between its genotype and the environment, while homozygous describes a specific type of genotype where an organism has two identical alleles for a trait. The phenotypic ratio is a term used to describe the ratio of different phenotypes that result from a genetic cross, rather than the genetic makeup itself.