Final answer:
Combinational controls, epistasis, and transcription initiation are the processes that work together to control the expression of single genes.
Step-by-step explanation:
Combinational controls work together to control the expression of single genes.
Several genes can contribute to aspects of a common phenotype without their gene products directly interacting.
They may function in complementary or synergistic fashions, requiring two or more genes to be expressed simultaneously to affect a phenotype.
This is known as epistasis.
Additionally, the expression of a single gene can be controlled at the level of transcription initiation, similar to how transcriptional control occurs in bacteria.