Biochemical and cytological studies of hybrids between HPRT-deficient rodent cells and lymphocytes or fibroblasts from Macropus robustus (the euro, M. r. erubescens, or the wallaroo, M. r. robustus, or hybrid animals) permitted assignment of Hpt, Pgk, and Gpd to the X chromosome of the euro and of Hpt, Pgk, Gpd, and Gla to the X chromosome of the wallaroo. Because of the rapid and extensive segregation of marsupial chromosomes from hybrids and the frequent fragmentation of retained chromosomes, these assignments were confirmed using extensive subclone and reversion analyses. The patterns of marker segregation in hybrids with deleted X chromosomes suggested a gene order of Gpd-Hpt-Pgk on the long arm of the euro X, and centromere-Gpd-Hpt-Gla-Pgk on the long arm of the wallaroo X. Marsupial STS was not detected, even in hybrids retaining an intact M. robustus X, suggesting that Sts is not borne on the X in marsupials.
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