Modifying and Regulator Genes T here are two classes of genes that can have an effect on how other genes function. They are called modifying genes and regulator genes . Modifying genes alter how certain other genes are expressed in the phenotype. For instance, there is a dominant cataract gene which will produce varying degrees of vision impairment depending on the presence of a specific allele for a companion modifying gene. However, cataracts also can be promoted by common environmental factors such as excessive ultraviolet radiation.
Regulator genes can either initiate or block the expression of other genes.
They control the production of a variety of chemicals in plants and animals. For instance, the time of production of specific proteins that will be new structural parts of our bodies can be controlled by such regulator genes. They are also responsible for changes that occur in our bodies as we grow older. Incomplete Penetrance S ome genes are incompletely penetrant . That is to say, their effect does not normally occur unless certain environmental factors are present.