Source: Jill U Adams via

Of two genetically identical mice, how can one be small and another fat? Research on epigenetic changes resulting from the environment can give us clues into obesity in mice–and humans.

Our genome contains all the information to make us who we are, but many of the details of our behavior and appearance are actually determined by gene regulation. A striking example of the power of gene regulation is seen in agouti mice, in which genetically identical twins can look entirely different in both color and size. For example, one mouse may be small and brown, but her twin sister may be obese and yellow. Another genetically identical sister may have a mottled look with both fur colors present and fall in the middle of the weight range. The genome of each of these mice is the same, but the gene expression obviously differs.


In these mice, the epigenome is what makes the difference. Picture a network of molecules that are intimately intertwined with nuclear DNA and that have the power to silence genes. The behavior of this entourage of molecules can be altered by the environment (or “nurture,” to use the terminology of the classic “nature versus nurture” debate) and can have a profound effect on an individual’s phenotype.

For instance, in normal, healthy mice, the agouti genes are kept in the “off” position by the epigenome, which attaches methyl groups to the corresponding regions of DNA, resulting in the DNA’s compaction to prevent transcription. In yellow and/or obese mice, however, the same genes are not methylated; thus, these genes are expressed or “turned on.” The turning on of this single gene results in an apparent freak of nature. Mice whose agouti gene is “on” are also more likely to suffer from diabetes and cancer as adults…Read More>>

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