BRAINCAKEEpigenetics and Disease
Because epigenetic tags decide which genes are switched on or off, abnormal epigenetic changes can cause disease. A gene that should be active may be silenced, or a gene that should be silent may be switched on. The DNA base sequence is normal, but the gene is expressed at the wrong time, in the wrong cells, or not at all.
Epigenetic changes can be triggered by environmental factors such as smoking, diet, stress and pollutants, and they build up with age. Unlike mutations, they are potentially reversible.
Example: fragile X syndrome. In fragile X syndrome, a repeated section of DNA in the FMR1 gene becomes much longer than normal and is heavily methylated. The increased methylation silences the gene, so its protein, which is needed for normal brain development, is not made. This causes learning difficulties.
Sign in free to see the rest of this lesson, the R.E.C.I.P.E. recall steps and the quiz
BrainCake is free. Make an account in seconds and pick up where this page stops.
Key terms in this lesson
- mutation
- A random change in the base sequence of DNA (a gene mutation) or in the structure or number of chromosomes (a chromosome mutation).
- genotype
- The genetic constitution of an organism, i.e. the particular combination of alleles it possesses.
- epigenetics
- The control of gene expression by heritable changes, such as histone modification and DNA methylation, that alter chromatin structure without changing the base sequence of DNA.
More in Control of Gene Expression
- RNA Interference (siRNA and miRNA)
- Epigenetics
- DNA Methylation
- Histone Acetylation
- Benign and Malignant Tumours
- Tumour Suppressor Genes
- Oncogenes
- Abnormal Methylation and Cancer
All 18 lessons in Control of Gene Expression · All AQA A-level Biology topics