AQA A Level Biology

Revision Notes

8.2.8 Epigenetics & Disease

Epigenetics & Disease

Inheritance of epigenetic modifications

  • Epigenetic imprinting is the DNA methylation of certain genes and it occurs during the formation of oocytes and sperm cells
  • A child, therefore, inherits two sets of DNA, one from the mother and one from the father, each with its own epigenetic imprint
  • Imprinting is reversible, therefore the maternal epigenetic imprints that are inherited by a male will become paternal imprints when his sperm are produced so that he passes on paternally imprinted DNA
  • Prader-Willi syndrome is an example of a condition with epigenetic links
    • The syndrome is caused by the silencing of an allele on chromosome 15
    • The severity of the syndrome depends on whether an individual receives the affected DNA from their mother or their father
    • If the mother is a carrier for the defective chromosome, individuals that inherit the chromosome do not develop the syndrome
    • However, if the defective chromosome is inherited from the father, the individual will develop the syndrome

Prader-Willi Syndrome_2, downloadable AS & A Level Biology revision notes

A family tree showing the inheritance of Prader-Willi Syndrome. An individual is only fully affected by the syndrome if they inherit the faulty chromosome from their father.

Epigenetic cancer treatment

  • DNA in human tumour cells have changes in DNA methylation and histone acetylation which causes tumour suppressor genes to be silenced and oncogenes to be activated
    • This leads to deregulation of the cell cycle and the formation of tumours
  • Some cancer treatments involve drugs that reverse the epigenetic changes through the removal of acetyl and methyl tags
    • Removal of methyl groups from the DNA of tumour suppressor genes will enable the genes to be expressed
    • The proteins produced can then regulate the cell cycle and stop tumours forming from faulty or cancerous cells
    • Removal of acetyl groups from histone proteins attached to oncogenes causes the DNA to wrap more tightly, silencing these genes
    • Reducing the expression of oncogenes stops cancer as faulty cells are able to die through programmed cell death (apoptosis) rather than continuing to replicate, causing cancer

Author: Amelia

While studying Biochemistry at Oxford University, Amelia started her own tutoring service, helping to connect Science tutors with students in her local area. Amelia has experience teaching the sciences and Maths at all levels to UK and international students and, as well as being our Biology Lead, designs revision resources for Chemistry.
Close

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Already a member?
Go to Top