Concordant segregation of the expression of the alpha subunit of human hexosaminidase A, human mannosephosphate isomerase, and pyruvate kinase was observed in somatic cell hybrids between either thymidine kinase-deficient mouse cells or thymidine kinase-deficient Chinese hamster cells and human white blood cells carrying a translocation of the distal half (q 22-qter) of the long arm of chromosome 15 to chromosome 17. A positive correlation was established between the expression of these human phenotypes and the presence of the distal half of the long arm of human chromosome 15.

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.

Somatic cell hybrids between thymidine kinase-deficient mouse cells and human fibroblasts carrying a translocation of the distal third of the long arm of chromosome 10 to chromosome 17 were studied for the expression of cytoplasmic glutamic-oxaloacetic transaminase. A positive correlation between the expression of human cytoplasmic glutamic-oxaloacetic transaminase and the presence of the distal third of the long arm of chromosome 10 was established.

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.