noun, plural: housekeeping genes
Housekeeping genes are those genes that are always expressed because they code for proteins that are constantly required by the cell, hence, they are essential to a cell and always present under any conditions. It is assumed that their expression is unaffected by experimental conditions. The proteins they code are generally involved in the basic functions necessary for the sustenance or maintenance of the cell. Examples of housekeeping genes include actin, GAPDH and ubiquitin.