Controlling Elements in the Mouse X Chromosome

number of X-autosome translocations have been described in the mouse, A which in the heterozygous female show a variegated phenotype for autosomal genes attached to the X chromosome ( CATTANACH 1961 ; RUSSELL and BANGHAM 1961 ; RUSSELL, BANGHAM and SAYLORS 1962).The primary cause in each instance was considered to be the inactivation of the associated autosomal genes (CATTA-NACH 1963; RUSSELL 1964) when the rearranged X is inactivated in the course of the normal process of X-inactivation (LYON 1961 ) .Evidence substantiating this hypothesis for one of the translocations has been obtained using both genetical and cytological tests (LYON 1963;OHNO and CATTANACH 1962).Supported in part hy U.