Gene action refers to the way in which genes exert their effects on the body. They could be dominant or recessive. Gene actions results in observable phenotype of an organism.
There are three types of gene actions:
Additive gene action
Additive gene action states that one allele of gene is substituted by other allele and it produces the same effect whether positive or negative.
Dominant gene action
When a dominant gene (A) is substituted via a recessive gene (a) and there’s no effect.
Epistatic gene action
In this sort of gene action, the presence or absence of an allele in one locus have an effect on the expression on any other allele in another locus. Epistasis can both exert additive effect or dominance.