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Seven strains of HeLa cells have been characterized by the number of chromosomes and the activity of the enzymes alkaline phosphatase, glucose-6-phosphate dehydrogenase, 6-phosphogluconic dehydrogenase, and lactic dehydrogenase . All seven strains were found to differ as to chromosome numbers and enzyme levels despite the fact that two strains were called HeLa and three were called HeLa S3 . Three strains were found to have a stemline in which greater than 60% of the cells demonstrated a single chromosome number, and this characteristic was stable for at least 6 months . A nomenclature for these clones has been suggested by the use of the stemline chromosome number as a subscript following HeLa . These three clones were, therefore, designated HeLa65 , HeLa71, and HeLa75 . Karyotypes were made of the stemlines of these clones and were compared with enzyme levels . Alkaline phosphatase showed the greatest variation from cell line to cell line with a 200-fold difference in levels, whereas glucose-6-phosphate dehydrogenase showed variation in activity over a 12-fold range, lactic dehydrogenase over an 8-fold range, and 6-phosphogluconic dehydrogenase over a 2-fold range .

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