a single phenotype or trait. There are however instances where a single gene can exhibit multiple phenotypic expression. Such a gene is called a pleiotropic gene. The underlying mechanism of pleiotropy in most cases is the effect of a gene on metabolic pathways which contribute towards different phenotypes.

Starch grain size and shape is under the control of one gene with two alleles B and b.

B shows incomplete dominance over b for starch grain size,while for shape of seed it shows dominance.