How is genotype best defined?

Genotype is best defined as the genetic information of an organism. It encompasses the entirety of an organism's genetic makeup, including all the alleles that the organism carries for specific traits. This genetic information can determine various physical traits, behaviors, and other characteristics by influencing how genes are expressed.

Understanding genotype is fundamental in genetics because it differentiates the actual genetic sequence and potential from the visible traits an organism displays, known as the phenotype. While physical traits (option A) relate to the observable characteristics resulting from the genotype, they do not represent the underlying genetic makeup itself. Reproductive cell characteristics (option B) are related but do not encompass the full scope of an organism's genetic information. Similarly, functional proteins produced (option D) are products of gene expression that result from the genotype, but they do not define what the genotype is. Thus, the best definition captures the essence of the genetic foundation of the organism.