The human osteocalcin gene was assigned to chromosome 1 by Southern blot analysis of DNAs from a panel of mouse-human somatic cell hybrids with limited numbers of human chromosomes and the complete complement of murine chromosomes. By Southern blot analysis of DNAs from mouse-human hybrids that retain specific segments of human chromosome 1, we have determined that the locus of the human osteocalcin gene is on the long arm of chromosome 1, distal (telomeric) to the -spectrin gene. Osteocalcin is a bone specific protein and it is note worthy that another osteoblast product, the bone/liver/placental alkaline phosphatase gene has also been mapped to chromosome 1.

We have studied the expression of mouse galactokinase in human-mouse somatic cell hybrids segregating mouse chromosomes. Since concordant segregation of the expression of mouse galactokinase and the presence of mouse chromosome 11 were observed in the hybrid clones, we conclude that the gene for mouse galactokinase is located on mouse chromosome 11. We have also investigated the expression of mouse galactokinase in somatic cell hybrids between thymidine kinase-deficient Chinese hamster cells and mouse peritoneal macrophages. The results of this study indicate that the expression of mouse galactokinase and thymidine kinase segregates concordantly, and, therefore, we infer that the gene for mouse thymidine kinase is also located on mouse chromosome 11.

The synteny of human mannose phosphate isomerase and pyruvate kinase and the assignment of the genes for these two enzymes to chromosome 15 were confirmed by analysis of 43 independently derived human-mouse hybrid clones. Hybrids between mouse cells deficient in hypoxanthine-guanine phosphoribosyl-transferase and human fibroblasts carrying an X/15 chromosome translocation were also included in this study.

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In human fibroblast cultures derived from adults, clones of cells with a common chromosome rearrangement have been widely reported. Cells derived from one of these clones have been used in hybridization experiments using mouse cells to localize the genes for β-glucuronidase and mitochondrial malate dehydrogenase on human chromosome 7. The results of this study indicate that the genes for these isozymes are located on the region pter→q22 of human chromosome 7.