The adrenal X-zone of mice: genetic analysis of its development with recombinant-inbred strains

The genetic aspects of development of the adrenal X-zone in female mice have been studied in the C57BL/6By and BALB/cBy inbred strains, their hybrids, and the CXB recombinant-inbred (RI) strains. Degeneration of the X-zone, with the accumulation of sudanophilic lipid, was well established in BALB/cBy females by the age of 60 days. Degeneration occurred later in C57BL/6By females, without lipid accumulation. The F1 hybrids showed fatty degeneration at 60 days. The CXB RI strains could be divided into four groups. Two resembled the parental strains and two had recombinant phenotypes. These observations, together with those on backcrosses of RI and F1 mice to the parental strains, indicated the existence of two genes controlling X-zone development. The two loci are provisionally named Exz-1 and Exz-2. In both cases the a alleles, present in BALB, showed dominance over the b alleles, present in C57BL.