phenotype

Your phenotype is everything about you that can actually be seen or measured: your height, hair colour, blood type, the proteins in your cells, even aspects of behaviour. It is the visible answer to the hidden question posed by your genes.

A phenotype emerges from the interplay between genotype and environment. The genotype provides instructions, but how those instructions play out depends on nutrition, climate, life history, and random events during development. The same set of genes can therefore yield different phenotypes under different conditions.

Phenotypes exist at every level, not just the obviously visible. The shape of a flower is a phenotype, but so are the concentration of a particular enzyme, the pattern of chemical tags on DNA, and the response of a cell to a drug. Modern genetics measures phenotypes from the molecular up to the whole organism.

A common pitfall is assuming that a shared phenotype implies a shared genotype, or the reverse. Two people can look alike for unrelated genetic reasons, and identical twins, who share a genotype, can still differ in phenotype because their environments and chance events were not identical.