Most of tlie work I shall discuss was done in collaboration with Dr, R. Dulbecco. This work centers around a study of tlie origin and natnrc of certain polio virus-resistant cell variants obtained in a tissue culture line of human neoplastic cells, tlic so-called strain IIeLa. My reason for choosing this study as the main subject of this paper is twofold: I hope that it will illustrate some of the problems that confront workers dealing with genetic changes in populations of animal cells grown in tissue culture, and, at the same time, give a fair picture of the methods of tissue culture that are at the moment available for the solution of these problems.
Sti-ain HeLa was derived by Gey and coworkers ('52) in 1951 from a tissue culture cxplant of a human epitheloid carcinoma of the cervix ; the strain has since been maintained continuously in tissue culture by serial passages. The chromosome constitution of strain HeLa is hcteroploid ; the chromosorncl numbers most frequently found range from about 65 to 90. Since the diploid chromosome number in man is 46, these nuinbcrs comprisc 110th hypotriploid and hypotetraploid cliromosorne constitutions. A certain fraction of the cell population always shows higher degrees of polyploidization. The possible relation between this heteroploidy and our findings will be discussed in grcatc.r clctail later.
Aided by n grant from the Nntioiial Foundation f o r Infantile Paralysis.