Youtube video about how to make transgenic flies:

Transgenic organisms are defined as a genetically modified organisms that contains DNA from two different genomes. A transgenic organism (or knock-in organism) contains a gene which is overexpressed for the purpose of ascertaining the gene function and location.  The method of creating a transgenic organism is the same as creating a knock-out organism.  A plasmid vector must be used for inserting the gene of interest into the genome.  The vector is introduced into the gametic cells of the organism and the experssion is confirmed in the offspring.