B' via epigenetic mechanisms. The B' and B-I alleles are considered to be epialleles because they are identical at the DNA sequence level but differ in the level of DNA methylation, siRNA production, and chromosomal interactions within the nucleus. Additionally, plants defective in components of the RNA-directed DNA-methylation pathway show an increased expression of b1 in B' individuals similar to that of B-I, however, once these components are restored, the plant reverts to the low expression state. Although spontaneous conversion from B-I to B' has been observed, a reversion from B' to B-I (green to purple) has never been observed over 50 years and thousands of plants in both greenhouse and field experiments. s Examples of environmentally induced transgenerational epigenetic inheritance in plants has also been reported. In one case, rice plants that were exposed to drought-simulation treatments displayed increased tolerance to drought after 11 generations of exposure and propagation by single-seed descent as compared to non-drought treated plants. Differences in drought tolerance was linked to directional changes in DNA-methylation levels throughout the genome, suggesting that stress-induced heritable changes in DNA-methylation patterns may be important in adaptation to recurring stresses. In another study, plants that were exposed to moderate caterpillar herbivory over multiple generations displayed increased resistance to herbivory in subsequent generations (as measured by caterpillar dry mass) compared to plants lacking herbivore pressure. This increase in herbivore resistance persisted after a generation of growth without any herbivore exposure suggesting that the response was transmitted across generations. The report concluded that components of the RNA-directed DNA-methylation pathway are involved in the increased resistance across generations. Transgenerational epigenetic inheritance has also been observed in polyploid plants. Genetically identical reciprocal F1 hybrid triploids have been shown to display transgenerational epigenetic effects on viable F2 seed development. In humans Although genetic inheritance is important when describing phenotypic outcomes, it cannot entirely explain why offspring resemble their parents. Aside from genes, offspring come to inherit similar environmental conditions established by previous generations. One environment that human offspring commonly share for nine months is the womb. Considering the duration of the fetal stages of development, the environment of the mother’s womb can have long lasting effects on the health of offspring. An example of how the environment within the womb can affect the health of an offspring is the Dutch hunger winter and its causal effect on induced transgenerational epigenetic inherited diseases. A number of