Researchers are always interested in how a biological molecule or process affects the entire organism, but often times becomes difficult to do so. So researchers have slowly evolved from looking at changes in the entire body to changes in an isolated organ, down to the molecular biology level. The cell culture arose from the need to investigate changes that occurred in the cellular environment.
Cell cultures attempt to mirror the environment that in-vivo cells are in.
The idea of the culture is to be able to manipulate the culture and monitor its effect on the cell population in question. Working with a cell or tissue culture allows the researcher an ample population of cells to reproduce the results received or to try other theories. What many researchers have found, however, is that as cells replicate they can produce mutated genes, which can present a cell phenotype that is unwanted. Also, most cells have a limited life span. To produce cells that live longer, a gene, is inserted into these cells.