Principles of Genetics and Breeding

3.1.4 Pleiotropism

Many and perhaps most of the biochemical pathways in the living organism are inter connected and often inter dependent. Products of one reaction may be used in several other metabolic schemes. Therefore, the phenotypic expression of a gene usually involves more than one trait.

• The phenomenon of multiple effect (multiple phenotypic expression) of a single gene is called pleiotropism. One gene has got its own effect on different parts or different characteristics of one and the same organism.
• The characters that are governed by the single gene are not related. To a hatchery manager, pleiotropic effects may be minor and insignificant if no economically important characters are altered.
• However, when pleiotropic effects either increase or decrease viability, productivity or market value, they become significant and can actually become more important than phenotype. Pleiotropism has been extensively studied in common carp, Tilapia aurea, channel catfish, etc.