What does "genotype" describe?

The term "genotype" refers to the genetic makeup of an organism specifically in terms of its alleles, which are the different forms of a gene that occur at a specific locus on a chromosome. Each individual inherits two alleles for each gene, one from each parent, and the combination of these alleles determines the genotype of the organism. This genetic composition plays a crucial role in influencing various traits and characteristics expressed by the organism, but it is distinct from the physical manifestations of these traits, which are described by the term "phenotype."

The other options describe different concepts. The physical expression of traits refers to observable characteristics resulting from the genotype interacting with the environment. A single trait relates to a specific characteristic that can be influenced by the underlying genotype, but it does not encompass the complete genetic makeup. Similarly, a characteristic of an organism may refer to any observable feature, further emphasizing the distinction between genotype and phenotype. Therefore, the definition of genotype as the overall genetic makeup of alleles is precise and underlines its foundational role in heredity and biological diversity.