Explain what is meant by epigenetics and how it can inhibit transcription.

Epigenetics is the process by which heritable changes in gene function are caused by environmental factors. These changes are not within the base sequence of our DNA but are in fact due to the chemical tags attached to the DNA and histones. Methyl groups attach to DNA and acetyl groups attach to histones. These chemical tags form a layer known as the epigenome; this layer determines the shape of the DNA-histone complex (chromatin). Two mechanisms lead to inhibition of transcription: decreased acetylation of histones and increased methylation of DNA. Decreased acetylation of histones leads to the histones becoming more positive increasing their attraction to the negative phosphate groups in DNA. Their association between DNA and histones becomes stronger causing chromatin to be tightly packed (known as heterochromatin) and therefore DNA is not accessible to transcription factors.Increased methylation to the cytosine bases in DNA prevents the binding of transcription factors to the DNA and also attracts proteins that condense chromatin (by inducing deacetylation of histones) forming heterochromatin making it inaccessible to transcription factors. Both of these inhibit the transcription of the genes within the heterochromatin.