3. Pleiotropy (or pliotropy) is the phenomenon in which a single gene conditions several different phenotypical traits. Some phenotypical traits may be sensitive to the pleiotropic effects (for example, inhibition) of other genes, even when conditioned by a pair of alleles in simple dominance.A mixture of pleiotropy and gene interaction is characteristic of these cases.1  Non-Mendelian Inheritance-Image Diversity: pleiotropy.ome phenotypical traits may be sensitive to the pleiotropic effects (for example, inhibition) of other genes, even when conditioned by a pair of alleles in simple dominance. A mixture of pleiotropy and gene interaction is characteristic of these cases. 1  Non-Mendelian Inheritance-Image Diversity: pleiotropy.