Housekeeping and tissue-specific genes A total of 575 housekeeping genes in the human genome were identified by Eisenberg and Levanon (30), and 7261 tissue-specific genes in the human genome were identified in the Tissue-specific Gene Expression and Regulation database (31). The list of housekeeping genes was downloaded from http://www.compugen.co.il/supp_info/Housekeeping_ genes.html (October, 2011). The list of tissue-specific genes was downloaded from http://bioinfo.wilmer.jhu.edu/tiger/ download/ref2tissue-Table.txt (October, 2011). The two gene sets contain 122 overlapping genes.