While all the cells have same genome and DNA, their transcription is cell and tissue type specific. For instance, eye cells will not make the enzyme that pancreas cells will make. mRNA for pancreatic enzymes will only be transcribed in pancreatic cells, it would not be made in any other cell types since the gene encoding those enzymes would remain "repressed" or rather switched off. Genes are turned on at molecular level and those molecules are also cell-type specific. Genes are tightly and precisely regulated based on tissue type, developmental stage as well as specific cell types.
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