How does the environment affect gene expression?

Let me begin by defining epigenetics: it is essentially the study of changes in gene expression that occur when the genome is not altered.

If we consider the case of two identical twins. Although their genomes should be the same because the zygote split into two identical parts, they will not look or behave the same when they meet in their twenties because of differences in their expressions, not differences in their genomes. This is because the two of them will grow up in different neighborhoods, receive different upbringings, attend different schools, etc.

Methylation is the process by which an enzyme adds a molecule, a methyl group, to the nucleotide cytosine, thereby muting certain genes and preventing the nucleotide from being coded in the form of proteins. Acetylation is the other specific process that regulates gene expression.

Acetylation adds an acetyl group to the nucleotide lysine, which causes the DNA to detach slightly from the histone and thus allows the gene to be expressed more easily by RNA polymerase. While methylation mutes genes, acetylation does the opposite. DNA is wrapped around histones, and the way DNA is wrapped around these proteins determines whether certain gene sequences can be expressed or not.

Furthermore, acetylation occurs continuously based on environmental factors, whereas methylation typically occurs only once and is more permanent. This is true for the majority of the genes in all the cells in our body because they all carry out specific functions.

I cannot say with certainty what causes each individual acetylation that occurs to affect gene expression; however, there are certain factors that are known to cause these processes: nutrition, climate, stress, diet, water quality and minerals, mental stimulation, daily routines and habits, etc.

I hope that answers your question. I learned all of this in AP Biology, and Bozeman Science was one channel that had a ton of useful videos. I think I watched one of theirs on epigenetics, so you might want to give that a look as well.

The environment can affect gene expression through various mechanisms such as epigenetic modifications, hormonal influences, and exposure to external factors like toxins or stressors. These environmental influences can alter the way genes are turned on or off, leading to changes in phenotype without altering the underlying DNA sequence.