The epigenetic instruction manual for the operation of the genome

The factors composing the instruction manual for the operation of the genome are, at least initially, of maternal origin and supplied in the egg; they are postulated to be reproduced only slowly, if at all, during growth. This would insure that, as the size of the animal increases, the concentrations of these factors would decline. The progressive decline is postulated to sequentially trigger appropriate master genes, each of which is turned on or off by precise concentrations of these regulatory factors; each master gene in turn specifies a specific pattern of subsidiary gene expression. This formulation can explain how a divided early embryo can grow into two nearly perfect but miniature larvae. The concentration of the regulatory factors would reach a nadir when growth stops and then gradually recover. The increasing concentration after puberty might tend to activate the genome in reverse order and thus contribute to senescence.