Cre-loxP system is a highly efficient system to create transgenic mice. It relies on the ability of Cre recombinase to bind and recombine sequences flanked by loxP sites. Using Cre-loxP system, it is possible to study gene function by either activating or inactivating a gene in a tissue-specific manner. The gene can also be inactivated if an inducible promoter is used, e.g. Doxycycline or Tetracycline-based promoters. The system has been used to create mouse models of several human diseases and has led to a better molecular understanding of many diseases.