Epigenetics

Epigenetics is a theory of Inheritance which suggests that gene expression within an organism can be altered by changes to the genome, without the DNA sequence itself being changed. This is mainly caused by the addition of specific chemical groups on to the genome, which can promote or inhibit the transcription of genes in to polypeptides. The genome alterations are considered to be heritable, therefore the changes in gene expression of an organism may affect their offspring in subsequent generations.

Histone modification is an example of an epigenetic change. Epigenomes are a layer of chemical structures that cover histone wrapped DNA. The epigenome wraps itself onto the inactive genes making it more compact and unreadable. Conversely, the epigenome loosens around the active genes allowing it to be read easily. This “highlights” specific parts of the DNA sequence. Another example is an epigenetic change in DNA methylation which is the addition of a methyl group to a part in a DNA molecule. This prevents specific genomes from being expressed. Different cells have different active genes despite having similar DNA sequences. For example, brain cells and liver cells contain the same DNA sequence yet the expressed active genes are different. Formerly, it was assumed that proper cellular development and distinction to occur in mammals, the epigenome was fully erased and reconstructed between generations. Now, however, incomplete removal of epigenomes in specific genes have been found, suggesting that certain gene profiles are inherited epigenetically.

References

  Utahedu. 3. Utahedu. [Online]. Available from: http://learn.genetics.utah.edu/content/epigenetics/ [Accessed 20 November 2015].