Abstract: The present invention is directed to the genetic transformation using multiple genetic sequences, wherein one of said genetic sequences encodes a polypeptide possessing excision activity, specifically a site-specific recombinase activity linked to a transgene unit and the use of this genetic construct in the removal of transgenes therefrom. The present invention provides the means to produce genetically-transformed organisms, in particular plants, in which selectable marker genes have been removed, thereby facilitating multiple sequential genetic transformation events using the same selectable marker gene. Accordingly, the invention provides the means for regulating transgene expression in genetically-manipulated organisms, for example to promote differentiation, de-differentiation, or any unidirectional developmental shift of a target cell which requires the time-specific expression of a particular gene.