Detection of small amounts of human DNA in human−rodent hybrids

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Abstract
A method of measuring semi-quantitatively small amounts of human DNA in irradiated human × mouse and irradiated human × Chinese-hamster somatic cell hybrids is described. One method uses molecular hybridization of cell DNA bound to nitrocellulose filters with a cRNA probe to Cot 0–1 human DNA. Alternatively hybrid cell DNA is reassociated in solution with a Cot 0–1 fraction of nick-translated human DNA. Formamide buffers give specificity to the reaction. The detection limit of the filter method is 0.2–0.5% equivalents and reassociation kinetics 0.005–0.1% equivalents of a human genome. Experiments with cell hybrids suggest that a fragment of repetitive DNA may be retained along with the selected genes after a cell fusion. In one case however, of a hybrid cell in which malignancy is suppressed, highly repetitious sequences were not found.