In the nonfiction book “Epigenetics” by Richard C. Francis the big idea is that biological systems interact, and that these systems and their interactions possess complex properties. The main idea is about how the interactions between external stimuli and gene expression result in speciation and divergence of cells, organs and tissues. The external and internal environmental factors can trigger responses in the individuals organs which in turn affect the entire organism. Richard Francis describes the nature of the epigenetic processes as a form of gene regulation. Epigenetic gene regulation is long- term gene regulation, so epigenetic alterations have long- term effects on gene behavior. This connects to the idea that gene expression is regulated by both environmental signs and developmental through stages. “Our environment affects the behavior of our genes both in the short and long term.” and “Environmentally induced epigenetic alterations that occur early in our lives and especially important (page 157). Specifically, Francis discusses ideas related to ways the environment of the fetus may affect its growth. For decades fetuses at risk for premature birth have been treated with a synthetic form of cortisol to promote their lung development, since respiratory failure is one of the main hazards of premature delivery. Doctors and scientists have become worried about the long- term effects of this treatment on the stress axis. In the past, fetuses that have received this treatment evidence lifelong hyperresponsiveness in the stress axis that results in greater incidence of heart disease and diabetes among other illnesses, as well as a reduced life expectancy. This is similar to the effects of maternal stress on the fetus, “When a mother- to- be is stressed ( this stress can come from many places- a bad marriage, social isolation, poverty)- extreme stress can lead to PTSD-she produces more cortisol than she otherwise would”(page 42). Some of this cortisol is spread to the fetus through the placenta. The heightened cortisol levels experienced by the fetus permanently changes the settings of the stress axis of the fetus in a way that makes it more sensitive and hyper responsive to future events. This segment stresses the idea that the external stimuli, such as the mothers level of stress during the time of her pregnancy can affect the genes expressed in the fetus when they are born. Another example is within a study of sea urchin embryos which found that the cell has a important part in an organism’s development. German scientist, Hans Driesch, found that if you remove cells from one part of the embryo and place them somewhere else, for instance from their lung area to mouth area their function changes. The cell’s identity does not come from predetermined genetic instructions inside it. It is the cues that a cell gets from cells around it that affect how the genes inside it behave. The idea that epigenetic processes have a random element is discussed in this book. Epigenetic inheritance adds a different view to the modern picture of evolution. The genome changes slowly, through the processes of random mutation and natural selection. Epigenetic inheritance can allow an organism to adjust its gene expression to fit its environment – without changing its DNA code. “For instance in the methylation at the agouti locus which affects not only coloration bus susceptibility to obesity, diabetes and cancer in mice( page 85)”. This is a random epigenetic change than can be inherited. In this case we can predict the health of a viable yellow mouse by its coat color, those viable yellow mice colartion are obese, diabetic and cancerous. Another process for which randomness is critical is X- chromosome inactivation and this adaptive, if it was not there would not be any X- women. Following the idea of epigenetic inheritance, some epigenetic alterations of gene behavior have effects that extend beyond an individual lifetime. External and internal environmental factors can trigger responses in individual organs that, in turn, affect the entire organism. It can be direct or indirect transgenerational epigenetic alterations. A direct transgenerational epigenetic alterations the epigenetic mark is transmitted directly from parent to offspring through offspring while an indirect alteration is when original epigenetic mark in the parent is reproduced with great fidelity in the offspring, much more common. For instance, in rats the effects observed in maternal behavior and stress response is much more indirect, while the alterations that influence these behaviors are created through social interactions that they both influence and are influenced by. One study was done on the Dutch famine cohort, a number of epigenetically altered genes were identified in blood cells. “The degree of methylation in these genes differed in those exposed to the famine compared to those who were not exposed”(page 7). They focused specifically on a gene that codes for “the hormone insulin like growth factor 2( IGFT)” which closely resembles insulin. IGF2 is a growth hormone one that promotes growth through cell division, its very important for growth of fetus. This was significant in demonstrating that the epigenetic effects of the fetal environment can extend over six decades. The nonfiction book “Epigenetics” by Richard C. Francis gives a thorough introduction to how epigenetics works. It descirbes studies involving external and internal stimuli that may effect the expression of genes, for instance within the stress on the fetus. It also describes the improtance of the randomness within epigentics as well as the long lasting effects of epigentic alterations. Epigenetic alterations may delay attempts to intervene after populationwide exposure to epigenetically active environmental factors. This implicates the need for a greater appreciation of environmental, nutritional, and epigenetic risk factors for human disease which have been seen to affect the human genome.