The human body has 210 types of cells each with the same DNA but with a different epigenome.
If our cells all have exactly the same DNA, then why do cells in our kidney do kidney things like piddle and get stoned. They don’t play Soduko or watch Dr Phil, like cells in the frontal cortex of the brain might do. Cells go from totipotent, to pluripotent,to differentiated, all with the same DNA but some of the genes have been turned off and some turned on. So a cell in an ovary would have certain genes turned on as influenced by it’s environment. It looks around and sees other cells applying mascara while driving 110 MPH or watching figure skating when it isn’t the Olympics and says “why not?” Yet take that same DNA and implant it in a testicle and you could teach it do testicle stuff by turning on the correct genes and shutting off others, (although testicles apparently are always turned on). Hence epigenomics is about to become much more important than genomics. Like having the same brand of TV throughout your house but being able to turn on different channels.
So again because of epigenetic influence and the turning on or off of certain genes, cells know whether they are an ovary or a testicle.
Again the unique epigenome in each cell directs the cell to interpret its genetic information differently in response to common environmental factors.
And here is the remarkable thing about it. What YOU do may well kill your…. grandchildren.
A turned on gene can be passed from generation to generation. You smoke and they might get cancer, not because they have even been exposed to smoke but because the smoke trigger has stimulated the epigene to shut off the tumor suppressor genes. This can leave a powerful imprint that can last for generations. Other example of epigenomics:
-Kids kept too clean get more eczema
-Men who smoke by age 11 will have sons who are obese by age 9 and shorter life spans
-Kids with poor memory can be stimulated with toys and attention and develop excellent memory that their progeny will have even if the progeny are not stimulated