"epigenetics:

the study of the chemical modification of specific genes or gene-associated
proteins of an organism. Epigenetic modifications can define how the
information in genes is expressed and used by cells. The term epigenetics
came into general use in the early 1940s, when British embryologist Conrad
Waddington used it to describe the interactions between genes and gene
products, which direct
development<http://www.reference.com/browse/direct%20development>and
give rise to an organism's phenotype (observable characteristics).
Since
then, information revealed by epigenetics studies has revolutionized the
fields of genetics and developmental biology. Specifically, researchers have
uncovered a range of possible chemical modifications to deoxyribonucleic
acid <http://www.reference.com/browse/deoxyribonucleic%20acid> (DNA) and to
proteins called histones that associate tightly with DNA in the nucleus.
These modifications can determine when or even if a given gene is expressed
in a cell or organism."

As I see it, epigenetics is everything that defines the phenotype (The
observable physical or biochemical characteristics of an organism, as
determined by both genetic makeup and environmental influences), which is
why I included bacteria. Bacteria is passed on and does influence the
biochemical characteristics of an organism. We all have specific skin
bacteria, stomach bacteria, etc. which are crucial to our health. We tend to
forget them when we talk about our "immune system", which I think is what
started this discussion.

And recent research showed that bacteria change DNA in the womb. So maybe
bacteria (passed from adult to offspring) have more of an influence on
passing on immunity than we currently think. It fits with the definition of
epigenetics, which seems to define the complete organism, not just DNA. (My
guess is the term tends to fit the researcher's concept and is as broad or
as narrow as they want. Mine is broad,)

Happy to be corrected, as always. Fun topic, since I am learning as we go.

Bill Truesdell
Bath, Maine

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