Each cell in the human body contains a nucleus with the same set of genes, the ribosomes, mitochondria, endoplasmic reticulum and Golgi apparatus are enclosed in a membrane mobile phone. Despite this, liver cells do not have much in common with nerve cells in appearance and function. This could be explained by cellular differentiation. Differentiation is a process of cellular specialization that begins with the installation of a genetic program, the precise determination is specific to the individual cell. The development of cellular differentiation involves the expression of specific genes, which control the biochemical functions linked to the cell type and which distinguish specialized cells (MacCorkle and Tan, 2005). Gene expression is the realization of hereditary information through transcription and translation. It is controlled by several complicated mechanisms. Changes in the developmental process from childhood to adulthood are the result of the programmed turning off and on of different genes. Even in adulthood some cells undergo differentiation, for example erythrocytes (red blood cells). Although the somatic cells of an organism have the same set of genes, in cells with different morphology and function (liver, nerve cells) a small and different part of the common genes is expressed