Genotype refer s to the complete genetic makeup of an organism.

Phenotype refers to the expression of a gene or genes carried by an organism.

Genotype directs phenotypic expression, but since all genes are not expressed all of the time, genotype is not always expressed as phenotype.  Two examples are lactose catabolism in E. coli and ecophenotypic expression of pigment in Serratia marcescens.

E. coli only produces the enzyme b-galactosidase (lactase) when lactose is present.  When lactose is depleted or not present, the sequence of genes controlling enzyme production is shut down.


S. marscescens produces the red pigment prodigiosin when incubated at a temperature range between 25 and 30 oC.  When incubated at 37 oC, the pigment is not produced or produced very little.