Question: How many genes in one chromosome will be switched on at one time? Is it the same in every chromosome of every cell?

Michaela Livingstone answered on 22 Jun 2010:

That’s a great question! The answer is: as many as are needed! There are a subset of genes that are needed by pretty much every cell for basic functions, like making energy and keeping the structure of cell the way it’s meant to be – those kind of genes are called house-keeping genes. There are hundred of these! But generally speaking, different cell types will have a different set of genes on and off, and even depending on outside influences and so forth, this might change that too! So the genes on in brain cells that make your legs move will be different than the set of genes on in a white blood cell.