Emma Lyree

What is epigenetics?

Epigenetics is everything that happens to the DNA (without actually changing the sequence of said DNA) that determines what can be transcribed and how accessible the actual DNA is for transcription and, in turn, what proteins can be made. The epigenome is flexible and changes with environmental changes. (In no way mutations, that would be a change in the DNA sequence itself)


Examples of epigenetics include methylation, acetylation, histone modifications, inhibitor proteins and everything that cause genes to turned off (not transcribed) or on (transcribed). Everything that happens to the organism as result of these genes being turned off and on is also called epigenetics. Examples of this included twins with identical DNA being different or having different feature. This also is seen with mice with identical DNA.

Cool.. How?


Methylation is adding methyl groups to the chromatin. Methyl groups allow all of the free DNA that is not wrapped up in nucleosomes to wrap around the Methyl groups. This leaves very little areas of free DNA where transcription can happen. When the chromatin is tightly packed like this it is called heterochromatin.

Or maybe acetylation?

Acetylation is what happens when acetyl groups are added to the histones in chromatin. The acetyl groups attach to the histone where the DNA would attach and causes the DNA to not be able to attach. This causes genes to be exposed and allows transcription to happen. When the chromatin is relaxed like this it is called euchromatin.

Mhmmm... Why tho?

How is your epigenome affected by environment?

Your environment determines your epigenome. Environmental "triggers" cause genes to be transcribed or cause cease the production of certain proteins.

Fat mice and skinny mice

The mice below have the same genome, but have completely different epigenomes. Here the trigger that made the difference between a fat yellow mouse and a skinny brown mouse was the chemical bisphenol and the DNA methylation around the agouti gene. Pregnant mice exposed to bisphenol had more yellow, obese pups.

Identical genome, different epigenome...

Oh wow! Too many citations to list!