How do you get a brain cell and a liver cell from the same genes?

Answer 1

After conception, the single fertilized egg begins to multiple and divide. Up to a point all of the cells are identical. That is why it is possible to have identical twins. If at some point the dividing cells increase their number so suddenly that a section of cells actually get bumped away from the main body of cells the second set of cells are identical to the first. If that second set can attach to the wall in time it will develop into an identical twin.

At this point the identical cells are called STEM cells. They have no individual identity and they are completely interchangeable.

It is a mystery that still puzzles researchers as to how the "triggers" turn on to tell one area of cells to become brain, another liver, another lungs, etc. But they do. The really amazing thing about that is that the body produces those cells even after we are born. I believe it occurs in the bone marrow.

Researchers are trying to find ways to coax those stem cells out of our body and place them into damaged areas to create new cells. Stem cells inserted into a dieing pancreas will become pancreas cells because they take on the identity of whatever cells they come into contact with.

They could be inserted into a diseased heart or lungs, or liver to grow new healthy cells.

They all carry the same genes because they come from the same donor.

It truly is a mystery....

Answer 2

Differing expression. Some turned on, some turned off. Some expression masked. Check out stem cell differentiation.