IAS General Studies Prelims Question No. 119
All cells contain the same genetic information, yet cells other than stem cells can not differentiate into various tissues. What is the possible reason for this?
[A] As cells develop their genetic makeup changes.
[B] As cells develop some genes are turned off permanently.
[C] Stem cells are the only cells that do not have an X or Y chromosome and can therefore go into either a male or female.
[D] Stem cells are the only cells that can be implanted
As cells develop some genes are turned off permanently. All of the cells within a complex multicellular organism such as a human being contain the same DNA; however, the body of such an organism is clearly composed of many different types of cells. What, then, makes a liver cell different from a skin or muscle cell? The answer lies in the way each cell deploys its genome. In other words, the particular combination of genes that are turned on (expressed) or turned off (repressed) dictates cellular morphology (shape) and function. This process of gene expression is regulated by cues from both within and outside cells, and the interplay between these cues and the genome affects essentially all processes that occur during embryonic development and adult life. This means that cells become specialized because the genes that are not required are switched off. Only the genes needed to make a particular type of cell work are switched on. So muscle cells only have the genes needed to make muscle cell proteins switched on. All the other genes, such as those needed to make blood cell proteins and nerve cell proteins, are switched off. But the stem cells are unspecialized and can develop into various tissues.