The influence of epigenetic modifications to the genome on the phenotype of the adult organism is now a tractable problem in biology. This has come about through the development of methods that enable us to study the methylation state of the DNA and the packaging of the chromatin at specific gene loci. It is becoming clear that early embryogenesis is a critical period for the establishment of the epigenotype. Furthermore, it appears that this process is sensitive to environmental conditions. This is a concern in light of the increasing use of artificial reproductive technologies throughout the world.