An interesting example of how environment can effect heritable changes via epigenetics is the agouti mouse strain. The fur color of this mouse strain depends on the diet of the mouse. Agouti mice whose diet consists of high levels of methyl donors develop a fur color that is passed on to the next generation of agouti mice (Dolinoy 2008). Variability in levels of DNA methylation at the agouti locus causes differences in coat color among genetically identical mice. Specifically, the maternal nutrition of a mouse affects the fur color phenotype of offspring by influencing the degree of DNA methylation at the agouti genetic locus. In addition, research shows that pregnant mice that intake diets with high level of methyl-donors, such as folic acid, delivered more offspring with severe allergic airway disease (asthma-like disease) compared to the one with lower methyl-donor intake (Hollingsworth, Maruoka et al. 2008).

Epigenetic processes also play a key role in genetic imprinting. Genomic imprinting describes how certain genes are expressed in a parent-of-origin-specific manner. In most cases the genes inherited from the mother and father play a role in the genetic outcome of the child. However, about 1000 of the 20,000 human genes undergo an epigenetic process whereby either the maternal or paternal gene is silenced. The exact mechanism for this change is not known at the present time.

Female X-Inactivation


In females there is a chromosomal event in which one of the two X chromosomes is inactivated by an epigenetic mechanism. After methylation, the inactive X chromosome is silenced and becomes transcriptionally inactive. This process occurs so that females, whose cells contain two X- chromosomes, do not have double the amount of X chromosome generated gene activity. In the male, there is only one X-chromosome.






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