Page "Heterozygote advantage" Paragraph 2

Often, the advantages and disadvantages conveyed are rather complicated, because more than one gene may influence a given trait or morph.

Major genes almost always have multiple effects ( pleiotropism ), which can simultaneously convey separate advantageous traits and disadvantageous traits upon the same organism.

In this instance, the state of the organism's environment will provide selection, with a net effect either favoring or working in opposition to the gene, until an environmentally determined equilibrium is reached.