Which term refers to the overall genetic composition of an organism?

The term that refers to the overall genetic composition of an organism is genotype. Genotype encompasses the specific alleles or combinations of alleles present in an individual's genetic makeup. It serves as the blueprint for the organism’s traits and characteristics, although these traits may not always be expressed due to environmental influences or interactions with other genes.

In contrast, phenotype refers to the observable characteristics or traits of an organism, which are determined by the genotype and other external factors. Heterozygous describes a specific condition regarding an organism's alleles, particularly when it has two different alleles for a given gene. An allele itself is a variant form of a gene that might lead to different traits. Understanding that genotype is the complete set of genes while phenotype is merely the manifestation of those genes provides clarity on the relationship between an organism's genetic material and its expressed features.