Mouse X and Y chromosomes, variant sex chromosomes, and mouse genotypes relevant to this study.

(A) The mouse Y chromosome contains ~90 Mb of male specific DNA and ~0.7 Mb constituting the pseudoautosomal region (PAR) situated at the end of the long arm. The PAR is the region of homology with the X that mediates pairing and recombination between the X and Y in normal males. The remaining non-pairing male specific part of Y (NPY) contains several genes and gene families. On the short arm (NPYp), there are single-copy genes: Prssly, Teyorf1, Uba1y, Smcy/Kdm5d, Eif2s3y, Uty, Dby/Ddx3y, Usp9y, Sry, duplicated gene Zfy (Zfy1 and 2), duplicated gene H2al2y, and a multi-copy gene Rbmy. The non-pairing region of the long arm (NPYq), representing ~90% of all NPY, contains mostly repetitive sequences, and encodes multiple copies of 5 distinct genes that are expressed in spermatids: Ssty1 and Ssty2, Sly, Srsy, Rbm31y [6]. Y*^X is an X chromosome derivative encoding PAR, X centromere and near centromeric region. Sxr^a is a sex reversal variant Tp(Y)1Ct^Sxr-a encoding almost intact NPYp complement but with Rbmy gene family reduced. Sxr^b is a Sxr^a derivative with a 1.3 Mb deletion that has removed the majority of the NPYp gene complement and created a Zfy2/1 fusion gene. (B) The mice used in this study and their Y chromosome contribution. The X chromosome located Eif2s3y and autosomally located Sry transgenes, are shown in light blue frames. The Zfy2 transgene, shown in brown frame, is located on the X chromosome in the Hrpt locus in close proximity to the Eif2s3y transgene. The genotype designations without the Zfy2 transgene are shown above the diagrammatic representation of sex chromosomes and with the Zfy2 transgene below them (brown font). Sxr^a and Sxr^b gene content is shown in A. n/a = mice with transgenic Zfy2 addition were either not produced or not examined in this study.