What are the definitions of monogenetic and polygenetic?

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The prefix mono refers to one, therefore, monogenetic inheritance involves the expression of a single gene. The prefix poly means many therefore, in polygenetic inheritance, several genes determine the expression of a trait. An example of monogenetic inheritance in pea plants is the trait of height. There is a single gene pair that determines height in gardens peas--and two alleles, tall and short. Depending on what combination of these alleles the plant inherits, this will in turn determine its height. Two tall genes or a tall and short gene produce tall offspring. Two short genes produce a short offspring. Tallness is dominant to short height and this trait follows Mendelian inheritance. Polygenic traits do not follow Mendelian inheritance and the phenotypes vary along a continuous gradient depicted by a bell shaped curve. That is because several genes combined effects produce a polygenic trait. Therefore, things like human skin color, height, are determined by the interaction of several genes and cannot be predicted as easily as one can with height in pea plants.

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