Through a series of human-mouse hybrids we have identified that two human chromosomes, 10 and 18, must be present for production of the pregnancy protein hormone human chorionic gonadotropin (hCG). Human choriocarcinoma cells producing hCG were hybridized to mouse cells. From 49 independent clones three hybrid clones continued to produce whole hCG. Chromosomal analysis was done on the 3 producer clones and 5 nonproducer clones. The additional 41 nonproducer clones were genetically characterized by isozymes. Only when chromosomes 10 and 18 were present in a clone would the whole hCG molecule be produced. Clones with only 10 or only 18 did not produce hormone. Nine subclones of a producer clone confirmed this observation. Three subclones retaining both 10 and 18 continued to produce hCG. This study demonstrated the need to use cellular chromosome data and population enzyme data to identify two chromosomes necessary for hCG production in heterogeneous human-mouse hybrids.
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