Genome, Genotype, Phenotype
The genome is the sum of the genetic material within a cell or an organism—thus, the total genetic endowment. By contrast, the genotype defines the genetic constitution, and thus biological capability, with regard to a specific locus (eg, individual blood groups or a specific single enzyme). Phenotype indicates the observable or manifest physical, physiologic, biochemical, or molecular characteristics of an individual, which are determined by the genotype but can be modified by the environment.
A clinical picture produced entirely by environmental factors that nevertheless closely resembles, or is even identical to, a phenotype is known as a phenocopy. Thus, for example, the pigmentary retinopathy of congenital rubella has occasionally been confused with a hereditary dystrophic disorder of the retina, RP. Similarly, amiodarone-induced changes in the corneal epithelium resemble those observed as cornea verticillata in the X-linked dystrophic disorder Fabry disease.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.