Expression of many genes in cells are requlated 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 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