Most of us have a rudimentary understanding of genetics, the science of how we pass traits down to our children through a gene blueprint, comprised of chromosomes, made of DNA in a double helix, etc. Most folks however may not have learned in science class about the term epigenetics. Why? The field was nearly non-existent until 10 years ago or so. In the term epigenetics, epi- refers to "over" or "on top of" genetics. That means that there are non-chromosomal structures and parts that are external to a person's DNA (anything that is not part a chromosome) can be affected by external or environmental influences. Dietary nutrients is one example. Toxic exposures another. However, our cells are also bathed in our bodies internally manufactured substances, like hormones and neurotransmitters (our body's natural chemical information carrying substances). We are only just beginning to understand which of these "chemicals" can affect, change or modify our DNA "switches" which turn our genes on or off.
The inherent structure of DNA does not get altered, it's just that the mechanism by which DNA and RNA produces the proteins of nearly about family reunion estranged family every cell function in our body, either goes into production or not. One mechanism that we know of is when a kind of chemical lid gets put on a DNA molecule (methylation), making it impossible for its code to be read and replicated.