Epigenetics = form of biological memory that doesn"t require change in dna sequence. Info that goes across mitotic division (eg. x chromosome inactivation, To make many diff cells, need them to remember what cells they were. Not every histone mark carries epigenetic info , we don"t know which ones do and which ones don"t. Some are transmitted onto next gen of cells but don"t know which example, just has to do with mitosis. Not all histone marks are transmitted to next generation. Chromatin is a thing, epigenetics is a process, ability of cells to remember things later on. Have diff parts of embryo that regulate transcription of various factors to determine which identity genes are expressed and refined, so you get embryo with many different segments. After many divisions, the cells remember their original function - remember and way by which they remember involves polycomb gene.