"Epigenetics cannot equal genetics, otherwise, why have the term at all?:

What is the definition of a gene?  The usual definition is a gene is a unit of inheritance.  I do not see anything in that definition that says a thing about DNA.  We need to think in terms of history.  In 1960 we had no clue what a gene was other than we knew they are located on the chromosomes and we were getting a half decent understanding of the chemical nature of chromosomes from a gross structure standpoint.  By about 1970 we were starting to understand the base code that specified amino acids to be placed in proteins and for a short time it was thought that genes simply specified proteins.  In the 1970s we also started to realize that most of a chromosome did not consist of genes that specified proteins and called it junk DNA.  By the 1980s we knew some genes did not make proteins at all, rather they made RNA as a final product.  But, we still called those sequences genes as they were units of inheritance that if defective resulted in abnormal individuals.  In the 90s we were starting to recognize that the junk DNA was not always junk and sometimes changes in the junk resulted in pheonotype changes, often by regulation of how much protein some protein coding gene produced.  So, we consider those changes in the so called junk as genes as they are a unit of inheritance.  About 2000 we started to get the first hints of something called epigenetics that resulted from chemical modification of either some bases in the DNA or even modifications of the histone proteins that DNA winds on.  Occasionally such chemical modifications are not erased during sex cell formation and are transmitted to offspring and can result in phenotypic changes.  In such cases they are transmitted as unit characters and fit the definition of a gene. Along the way we have also recognized switches, promoters and inhibitors that routinely regulate protein coding functions and figured out that if all that existed was protein coding genes they would be useless.  To be useful they needed to be controlled.  A protein coding gene all by itself can not even make protein.  It is in a perpetual off state.  Those can all act as unit characters and are rightfully called genes.  I doubt we are any place close to the end of the line in understanding all of the things that go into making genetics work that are rightfully all called genes.  So, why have a term like epigentics at all?  It is a classification term just like the named sub species of bees are a classification system. It fits right in with promoters and switches and RNA only genes which are also classification terms.  I am sure more classification terms will be added as new findings are made.

It does get confusing as when people count genes they generally count only those things that make proteins that are useful or maybe those that make useful proteins plus the hand full of RNA only genes.  When you read that humans have 22,000 genes that is the way the number is counted.  This count does not even include all the pseudo genes that make lots of protein that is useless and promptly degraded and the components reused.  There are some 20,000 of those known in humans as I recall.  But, they do not effect phenotype so are not considered genes.  All the things like switches and promoters are not counted as we can not look at a DNA sequence today and even recognize them with some exceptions. And epigenetics is in such a state of infancy we hardly know much more than it exists and is really, really important and without it life would not exist.

Dick

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