Like most machines in Advanced Genetics, the DNA Breeder requires energy to function. The energy must either be Redstone Flux (RF), Energy Units (EU), or energy directly from Advanced Genetics' Combustion Generator.
Place a Gene with a trait in the right slot of the DNA Breeder GUI. The machine will display how many extra Genes will need to be inserted to complete the Gene. Inserting Basic Genes into the DNA Breeder in the left slot of the GUI will add 1 point, while a Gene with the same trait as the one being completed will add 2 points.