Pleiotropy is defined as the property of a single gene locus to effect two or more unrelated phenotypes. If two or more different phenotypic traits segregate together with a particular mutation, that particular mutation is called pleiotropic. "Genuine" pleiotropy as defined by Hans Gruneberg is charecterized by two distinct primary products arising from a single locus and "Spurious" pleiotropy results when one primary product results in different phenotypes through a series or cascade of events.

Recent advances in the understanding of transcription, translation and protein synthesis have enabled us to understand the molecular mechanisms of pleiotropy, one of the mechanisms of pleiotropy is alternate reading frame and alternate splicing of mRNA during protein synthesis which could result in different proteins. Since the information for the two different protiens is contained in one locus and recombination events could not separate the two protein products the mechanism of alternate frames and alternate splicing fits the criteria of pleiotropy at mRNA level.