<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>Genes that are expressed at a fairly consistent level throughout the cell cycle and from tissue to tissue. Usually involved in routine cellular metabolism. Often used for comparison when studying expression of other genes of interest.</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>