What is the difference between pleiotropy and polygenic inheritance?

What is below is quoted from the following site: What is a Polygenic Inheritance? (http://www.wisegeek.com/what-is-a-polygenic-inheritance.htm) You might want to visit the link for a good read and study.


The term “polygenic inheritance” is used to refer to the inheritance of quantitative traits, traits which are influenced by multiple genes, not just one. In addition to involving multiple genes, polygenic inheritance also looks at the role of environment in someone's development.


In pleiotropy, on the other hand, one gene is responsible for multiple things. Several congenital syndromes are examples of pleiotropy, in which a flaw in one gene causes widespread problems for a person. For example, sickle cell anemia is a form of pleiotropy, caused by a distinctive mutation in one gene which leads to a host of symptoms. In addition to causing mutations, pleiotropy also occurs in perfectly normal genes, although researchers tend to use it to track and understand mutations in particular.

What is the difference between pleiotropy and polygenic inheritance?
Simply put, they are in a sense opposites.
A pleiotropic gene is a gene that affects more than one trait, while a polygenic trait is the result of the interaction on several genes.