Eli5: How does a single cell multiply into exact copies of itself yet somehow knows to start building into different body parts? They are all in the same environment with the same DNA yet behave differently.

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Eli5: How does a single cell multiply into exact copies of itself yet somehow knows to start building into different body parts? They are all in the same environment with the same DNA yet behave differently.

In: Biology
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Each cell has all the DNA, however based on external signals the cell activates certain enzymes that read specific DNA to become whichever organ.

Theoretically, you can introduce a reading enzyme from a liver cell to a heart cell and that enzyme will read the heart cell DNA to make liver stuff.

Cells have information in their dna on how they should behave.

Depending on different triggers like environmental conditions, they can trigger different sequences of those instructions. When organism starts to develop, there are instructions on how cells should divide, like what becomes an arm, what becomes a leg based on how many divisions been done and from what point. Then they just follow these instructions.

There are cases where these instructions can fail, leading to bit missing, or it being in the wrong place.

We can actually monipulare these intructions, and have on things like fruit flies. Where you can make a limb grow to a different place.

Because they’re not in the same environment. Once your original cell divides enough times, you’ve become a ball of cells.

Originally yes, the new cells were in the same environment but now, as a ball, you have got inside cells surrounded by other cells and outside cells forming the surface of the ball.

The inside cells start doing different things compared to the outside cells because they’re in a different environment.

Because of this, the ball changes shape and stops being bally and round and starts having a different elongated bean shape.

Now the outside cells are different from each other. Some are at the ‘top’ and others at the ‘bottom’ and they start doing different things. Inside cells nearer the top outside cells start doing things differently to the inside cells near the bottom outside cells.

This continues with each iteration of change creating new environments for the cells which now react differently to their parent cell, and so on and so forth until you have all your body parts.

Epigenetics. The cell has different *structures*, and based on the structures of both the cell and its neighbors, it knows what DNA to activate, and which cell type to become. Cells know which cell type to become based on what the cells around them are, and what stage in development they are in.