You have learned that each one of your cells contains one copy of your unique genome. Given the fact that all the cells in one human contain the same DNA, how is it possible that our cell types are so different, resulting in four different tissue types?

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Explanation:

Yes, the cells in one human contain the same DNA. However, during gene expression, not all the genes are expressed for every cell. Only a specific region of the DNA is expressed in cells and the cells in which the same DNA region is expressed end up performing similar roles in the body of organisms. The portion of the DNA that is expressed dictates the function which these cells will serve. This is called the differentiation of cells.