Expression of many genes in cells are requlated H ed housekeeping genes: expresse constitutively, essential for basic processes involving in cell replication and growth Inducible genes: expressed only when they are activated by inducers or cellular factors4 Housekeeping genes: expressed constitutively, essential for basic processes involving in cell replication and growth. Inducible genes: expressed only when they are activated by inducers or cellular factors. Expression of many genes in cells are regulated