1

I⁺ Z⁺ Y⁺

−

+

−

+

I⁺ is inducible

2

I⁻ Z⁺ Y⁺

+

+

+

+

I⁻ is constitutive

3

I⁺ Z⁻ Y⁺/F′ I⁻ Z⁺ Y⁺

−

+

−

+

I⁺ is dominant to I⁻

4

I⁻ Z⁻ Y⁺/F′ I⁺ Z⁺ Y⁻

−

+

−

+

I⁺ is trans-acting

Note: Bacteria were grown in glycerol (no glucose present) and induced with IPTG. The presence of the maximal level of the enzyme is indicated by a plus sign; the absence or very low level of an enzyme is indicated by a minus sign. (All strains are O⁺.)