Thus genes carry the blueprints to make proteins in the cell. Every cell in the body has the same genetic information; what makes cells, tissues and organs different is that different sets of genes are turned on or expressed. More evidence has supported the view that inheritance is not just about which genes we inherit but whether these are switched on or off is a whole new frontier in biology. It raises questions with huge implications, and means the investigation is on to find what sort of environmental (such as gene-nutrients or other chemicals interactions) effects can affect these switches in evolutionary processes. Such non-DNA based forms of heritable variations have been reported to change the way in which genes are expressed or maintained. This epigenetic inheritance is the transmission of information from a cell or multi-cellular organism to its descendants without that information being encoded in the nucleotide sequence of the gene......If this were shown to be the case, then some instances of evolution would lie outside of the typical Darwinian framework, which avoids any connection between environmental signals and the production of heritable variation.
A pregnant woman's dietary deficits increase her offspring's risk of diabetes, stroke and heart disease later in life. These startling scientific discoveries illuminate the emerging field of epigenetics, in which single nutrients, toxins, behaviors or environmental exposures of any sort can silence or activate a gene without altering its genetic code in any way.
Fleeting exposure to anything that influences methylation patterns during development can change the animal or person for a lifetime. Methyl groups are entirely derived from the foods people eat (folate, methionine, vitamin B12, selenium, Zinc, vitamin A, whereas alcohol, arsenic etc have negative effects). Our current understanding of genomic imprinting indicates that imprinting centres are differentially marked by DNA methylation (and probably, chromatin modifications) during gametogenesis. This phase of establishment of epigenetic settings is preceded by an erasure phase, where the settings inherited from the previous generation are erased in primordial germ cells.
Epigenetics represents a huge opportunity to study an alternative pathway that explains why individuals respond differently to environmental signals. For example, why does one identical twin develop schizophrenia and not the other? Why do certain disease genes seem to affect some people more than others? Why do complex diseases like autism turn up in more boys than girls? For answers, epigeneticists are looking at biological mechanisms other than mutation that affect how genes function.. The genes on one of the two X chromosomes in each female cell are silenced by methylation (dosage). Darwin's theory, though it succeeded in profoundly shaking scientific opinion regarding the development of life, could not explain the source of variation in traits within a species. There are different patterns of gene activity in humans that are the consequences of different epigenetic influences; these definitely induce differences in development of the body, and may bias the development of the brain in various subtle ways, but any intrinsic biological differences in the operation of the adult brain are also influenced by social and cultural factors.
Nutrition is one of the most important players in the epigenetic repertoire. For example, maternal diet during pregnancy is very important in fetal development but in ways that are not yet fully understood. The maternal reproductive tract, arguably, is the environment most critical to the developing mammalian embryo. Its metabolic and physiologic characteristics modulate the zygote's development through all embryonic stages until birth. Indeed, the conditions in the embryo's immediate milieu seem to determine many characteristics and susceptibilities of the adult organism.
With the help of some obese yellow mice, we now know how mother's diet can permanently alter the functioning of genes in her offspring without changing the genes themselves. The epigenetic state of the the agouti viable yellow locus, containing a gene contributing to coat colour in mice can be manipulated by latering the diet of the pregnant female. The unusual strain of mouse carries a kind of trigger near the gene that determines not only the colour of its coat but also its predisposition to obesity, diabetes and cancer. When pregnant mice were fed extra vitamins and supplements, the supplements interacted with the trigger in the fetal mice and shut down the gene. As a result, obese yellow mothers gave birth to standard brown baby mice that grew up lean and healthy. The research is a milestone in the relatively new science of epigenetics, the study of how environmental factors like diet, stress and maternal nutrition can change gene function without altering the DNA sequence in any way. Such factors have been shown to play a role in cancer, stroke, diabetes, schizophrenia, manic depression and other diseases as well as in shaping behavioral traits in offspring. A Dutch famine near the end of World War II led to an increased incidence of schizophrenia in adults who had been food-deprived during the first trimester of their mothers' pregnancy. Malnourishment among pregnant women in the South during the Civil War and the Depression has been proposed as an explanation for the high incidence of stroke among subsequent generations.