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If every cell has the same DNA, how do they decide which part of the body to be?

If every cell has the same DNA in there how do they decide which part of the body to be?
Nicola from Cambridgeshire (Aged 5-14)

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2 Responses

  1. In the very early stages of development, the fertilised egg is a specilised cell that has the potential to become any type of cell in the body. The way in which cells in the embryo become mature cells of different types (called differentiation) depends on which of their genes they switch on (called gene expression), at what time and for how long. There are thousands of different signals, encoded in the genes, involved in controlling these processes. Cells use these to ‘talk’ to each other within a developing embryo to make sure that all the right bits develop in the right places.

  2. While it is true that every cell in the body does have the same DNA, it is not just the fact that the DNA is there in the cell that determines what type of cell a particular cell is, or where in the body that cell exists.

    It is rather which individual genes on the DNA are activated or “expressed” that determines the fate of each individual cell. Not all genes are expressed in all cells.

    It is the differences between how, when and where different genes are switched on that determines the formation of different types of cells.

    As cells divide in the developing embryo, different genes are switched on in the new cells that are formed. The products of gene expression, the proteins, can act on neighbouring cells to regulate gene expression in these adjacent cells.

    The types of genes that are switched on and therefore the types of proteins that are found in each cell determine what type of cell it becomes, whether it be a skin cell, a blood cell or a liver cell.

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