Various scientific epidemiological studies have revealed that most adults are highly prone to diseases, and this exposure is basically associated with adverse environmental conditions including famine (Heijmans et al 17046). This precisely targets those individuals who are prenatally exposed to famine or hunger, which is considered to be one of the environmental co-factors which play a significant role in heredity (Heijmans et al 17046).
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The early developmental stages of an individual especially for the mammalian species, is the most vital and crucial period in which most establishment of the epigenetic mark occurs especially when exposed to harsh environmental conditions. This epigenetic mark can be transferred from parent to the offspring or in other words can be inherited.
Mechanisms of epigenetic gene regulation
Epigenetic inheritance can be defined as a scientific study of inheritable changes in gene expressions, which may occur due to changes occurring on the underlying DNA sequence and which may also occur due to other external mechanisms altering the gene expression (Ghose).
Epigenetic inheritance again disqualifies the idea that inheritance only occur via the DNA contrary to genetic inheritance where it’s believed to be so (Ghose). This is because; it has been observed in many occasions that according to genetic inheritance, the parent passes genes to the offspring’s. But when it comes to epigenetic inheritance it is revealed that even the parents acquired life experience can be transferred to the offspring’s in form of epigenetic tags, which can further be passed on down to future generations (Ghose).
The other difference between genetic inheritance and epigenetic inheritance is that, despite the fact that the DNA molecule is known to be very stable; it is rarely subjected to modification contrary to the epigenetic tags which are weak and prone to many changes occurring over a given period of time once it’s subjected to any environmental influence (Ghose).
This is the reason as to why twins have slight lifestyle variations though they are monozygotic (arise from one zygote) with identical epigenomes (Ghose). Even though the twins have identical epigenomes, several studies have revealed that these epigenetic tags eventually are considered to undergo changes over a period of time. The major forms of mechanisms that lead to epigenetic modification include DNA methylation and Histone deacetylation or modification (Heijmans et al 17048).
Nevertheless, most phenotypic expression carried by offspring’s from the parent can be altered by any heritable gene transcription, which in most cases result to these epigenetic effects (Heijmans et al 17048). Moreover, Histone proteins which are referred to be tiny spherical granules on which the DNA double helix strand wraps around, will automatically results to visual changes (at the phenotypic stages) in gene expression (Heijmans et al 17048).This is due to the slight changes of the DNA wrapping around the Histone.
Based on this process “post translational modification of the long chains amino acids” (which are the building units for the Histone) will result in alteration of the shapes of the Histone sphere (Heijmans et al 17048).
Furthermore, the DNA strand which may or may not be completely unwound during the normal stages of DNA replication will possibly result to the transfer of the modified Histone to each new copies of DNA produced during the cellular growth stages (Heijmans et al 17048). Furthermore, these new Histone once formed will act as templates initiating and reinforcing any new modifications to be copied to all differentiating cells which will remain in this new shape without reverting back (Heijmans et al 17048).
One recent study which sought to investigate the environmental influence which can result in persistent changes of the epigenetic mark was done through a case study which based on individuals who were prenatally exposed to famine. During this period of famine, medical personnel present at that time had kept reliable records of all individuals who were prenatally exposed to hunger, so that they would make a follow up later during the study; in what would later become a cohort study
Gestation exposure (Timing)
A case study was conducted on sixty two individuals who had previously been exposed to famine during their gestation period, just to investigate and evaluate the influence of timing on DNA methylation; these people constituted the case group of the sample (Heijmans et al 17049).
Furthermore, when determining whether IGF2 DMR methylation depended on timing, more studies were conducted on the periconceptional and late exposed groups who were analyzed together in a single model; the results confirmed that periconceptional exposure was basically associated with lower methylation, whereas the late exposure was not (Heijmans et al 17049). This was statistically and significant evidence which revealed presence of interaction between timing and environmental exposure (Heijmans et al 17049).
Moreover, the mean weight of sixty two individuals who were previously exposed to famine in their late gestation period was measured; it was again proved that the total mean which was calculated was 3126g; 296g lower than the mean of reference births recorded in 1943 in the very same institution which was 3422g (Heijmans et al 17047). This lower birth weights occurred as a result of famine during the previous hunger winter period, not withstanding the fundamental relationship between IGF2 DMR methylation (Heijmans et al 17047).
This experiment was based on determining presence of any correlation between age and IGF2 DMR methylation; comparatively, the 122 control individual analysis revealed that age 10 was identified to be associated with 3.6% low methylation modifications across all the age group sampled. (Heijmans et al 17047).
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Periconceptional exposure of an individual especially to famine was deduced to be associated with variation in IGF2 DMR methylation, which eventually was observed in adulthood among the subjects; to confirm this laboratory analysis was done which validated the findings.
The results confirmed that “all CpG sites except one was significantly less methylated among all quantified periconceptionally exposed individuals as compared to their offspring’s which was at 0.488” (Heijmans et al 17047); consequently, for those siblings not exposed it was observed to be at 0.515. Finally, basing on the results it was deduced that periconceptional exposure was associated with 5.2% lower methylation occurrence which was ultimately independent of sex (Heijmans et al 17047).
Hypothesis testing and supportive evidence
Basing on the argument, the data provided completely support the hypothesis; that environment strongly contributes to epigenetic inheritance, more supportive evidence is availed when a study on twins was conducted (Ghose).
Twins who share identical genes, with similar methylation patterns which have been inherited from their parents, still ended up being so different (Ghose). Furthermore, in most cases; twins who emerged from same zygote (monozygotic twins) exhibited such scenarios where one could suffer from a disease like diabetes or cancer while the other remains perfectly healthy (Ghose).
This is attributed to be the impacts of environmental influences, which eventually results in adaptation of different epigenetic variability; this epigenetic variation in terms of methylation pattern arises due to insignificant, “random changes in DNA methylation” which collectively accumulates after each cell division causing a major change (Ghose).
The most current studies have revealed that these cases of associations between DNA methylation and that of periconceptional exposure during the early developmental stages are also common in modern societies probably because of the present lifestyles coupled with environmental factors. This evidently includes reported cases of over nutrition and assisted reproductive methods and technologies; all being measures which give rise to similar associations
Though various research studies have been done on the subject matter, there is no conclusive evidence to suggest whether this epigenetic inheritance is real or not; nevertheless most evidence indicate this epigenetic inheritance is possible.
This is because of the fact that these findings have further explained many strange patterns of inheritance, in which many geneticists have been puzzling on over decades to uncover. The twin evidence discussed in this paper is one such vital proof that shows how epigenetic and DNA methylation can occur catalyzed by environmental influence (Learn.genetics.com).
Finally, one most important notation concerning epigenetic inheritance is that the most crucial stage in which the establishment of epigenetic marks can occur is during the early embryonic development stages of the organism. This was practically proved through an experiment carried out on mice, whereby when culturing the preimplantated mice embryo, it was revealed that the epigenetic marks were susceptible to environmental factors especially nutrition during their early days of development.
Ghose, T. An epigenetic inheritance, 2009. Web.
Heijmans, T., Tobi, W., Stein, D., Putter, H., Blauw, G., Susser, S., Slagboom, E. & Lumey, H. “Persistent epigenetic differences associated with prenatal exposure To famine in humans.” Newyork state psychiatric institute, 105 (2008): 44. Print.
Learn.genetics.com. Epigenetics and Inheritance, 2011. Web. Retrieved from https://learn.genetics.utah.edu/content/epigenetics/inheritance/