14 Oct 2014


An organism’s observable characteristics or traits. A phenotype is the physical manifestation of an organism and includes its observable structure or appearance – such as a person’s weight or the color of their eyes and hair – as well as function and behavior. A phenotype is influenced both by an organism’s genotype and by the environment. Genotype refers to the overall genetic constitution or makeup of an organism. The genotype – the internally coded and inheritable information carried by an organism – holds the instructions used by the organism’s cells to produce the external manifestation or the phenotype. Phenotypes cannot be directly inherited, since they are influenced by the environment.

As an example of phenotypes, consider two identical twins who are separated at birth and grow up in very different families in cities very far apart. Although both twins have the same genotype, environmental factor will have a significant effect on their phenotypes.

Thus, if one twin grows up in an affluent family, and the other grows up in an impoverished family, their phenotypes are likely to be markedly different. The twins may have been virtually identical at birth, but as they grow up, their phenotypes will be greatly influenced by their respective environment. This may mean that their physical and other traits such as weight, mannerisms, disposition, and behavior will differ significantly. But if they had grown up in the same family, their phenotypes may have been quite similar.

It should also be noted that the phenotype does not stay constant throughout an individual’s life, but changes due to environmental factors and the effects of aging.

In the area of drug development, phenotypic screening – which involves assessing and analyzing the effects or phenotypes that a compound induces in cells or organisms – used to be the preferred method to identify new drugs. However, identifying a specific molecule or molecules after initial phenotypic screening often proved to be a slow and laborious process. As a result, this type of screening has been overtaken since the 1980s by target-based screening, which is a more focused approach.

Covid-19 – Johns Hopkins University

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