"Epigenetics is the study of epigenetic inheritance, a set of reversible heritable changes in gene function or other cell phenotype that occur without a change in DNA sequence (genotype). These changes may be induced spontaneously, in response to environmental factors, or in response to the presence of a particular allele, even if it is absent from subsequent generations."
That is a lot of words to say that a bunch of material located on the strands of DNA but not the DNA itself determines which genes are turned on or off. The genes are The DNA but the material that surrounds them has lots to do with how or what they express. OR! material that is changed during the life of one person is passed on to that person's descendants. Sometimes that works for three or four generations or more. That is a whole lot like the old Lamarkian Theory. It also means that some of the things we do, what we eat, what is in our environment will determine some of the characteristics of our descendants. This idea would have gotten you thrown out of a college biology class in the 1960's. Do a Google search and find out what you think of it.