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3.3 Epigenetics

Genetic Determinism

The belief that our biological nature, or genotype, is entirely responsible for an individual’s phenotype is also known as “genetic determinism.”  There is no longer a debate over whether nature or nurture exerts the most significant influence on phenotype. We now know it is a combination of the two because our experiences and exposures can influence the expression of genes. The article by Harden (2023) in the optional reading list of 3.8 explores the differences between genetic determinism, essentialism, and reductionism.

Key points from Harden (2023)

Genetic determinism, essentialism, and reductionism influence how people discuss human genetics, but they are often misunderstood or misused and can lead to everyday discrimination.

  • Genetic determinism is the belief that a person’s traits are entirely determined by their genes, regardless of the environment. In other words, this belief implies that knowing someone’s genes would allow you to predict their traits with certainty. Genetic determinism is not the same as heritability. Genetic determinism suggests a causal relationship between genotype and phenotype. Heritability is a statistical measure of the variance due to genetic differences in a population.
    • Example: Having five fingers is often considered genetically determined. However, most traits, like how much education someone completes, are influenced by many factors.
    • Implications of misunderstanding and misuse: This can lead to the false idea that social inequalities are unchangeable.
  • Genetic essentialism is the idea that DNA gives things an unchanging “essence” that defines what they are. Essentialism views group membership as based on biology, as opposed to social constructs, with distinct boundaries, stability, and exclusivity.
    • Example: It assumes that people with certain traits, like skin colour, also have a more profound genetic similarity.
    • Implications of misunderstanding and misuse can lead to prejudice and stereotypes.
  • Genetic reductionism is the belief that understanding genes alone can fully explain complex traits or behaviours.
    • Example: It suggests that studying genes is enough to explain conditions like depression. Most scientists support looking at multiple factors, including social and environmental influences.
    • Implications of misunderstanding and misuse: It can overemphasize genetic research while ignoring other important factors.

Epigenetics

Epigenetics (sometimes called epigenomics) focuses on changes in DNA that do not involve alterations to the underlying sequence. The term “epigenetics” means above (epi) the gene. The DNA letters and the proteins that interact with DNA can have chemical modifications that change the degrees to which genes are expressed (referred to as gene expression) causing alterations to the normal production of proteins from these genes. Certain epigenetic modifications may be passed on from parent to daughter cell during cell division or from generation to generation. Others are acquired throughout life. The collection of all epigenetic changes in a genome is called an epigenome.

Read

Fessele, K. L., & Wright, F. (2018). Primer in genetics and genomics, article 6: Basics of epigenetic control. Biological Research for Nursing, 20(1), 103–110. https://doi.org/10.1177/1099800417742967 .

Access Fessele & Wright (2018) article via the Georgian College library (login required) Access the Fessele & Wright (2018) article via another institutional library - authentication required.

Same Genome, Different Cell

To understand epigenetics, we must first consider our genome – our DNA. Nearly all the cells in our body contain an identical copy of our genome, which includes the instructions to build and repair us. Yet, despite having the same set of instructions, cells from different tissues and organs can be very diverse. They may look completely different and have very different functions.

Look at the images below to see how four different types of cells can be different despite having an identical genome.

So, if the genome is the same in all these cells, why are they different? The answer is in how the genes are regulated (how they are used in other cells). This process differs between cells and is partly controlled by something called epigenetics.

 

This image has four sections. From the top left, moving clockwise, the first image shows an immune cell, the second a nerve cell, the third, an epithelial cell, and the fourth a muscle cell. These are illustrations to show that there can be differences in cell types with the same genome.
Differences in cell types despite the same genome. Source: Genomics Education Programme, CC BY-NC 4.0

Types of epigenetic modifications

Many different forms of epigenetic modification take place in, or ‘tag,’ an organism’s genome. – see the gallery below.

The most researched epigenetic modification is DNA methylation, which acts like a dimmer switch, altering gene expression. A chemical called a methyl group attaches to a region near the start of a gene and prevents it from being expressed or reduces expression. For example, methylation of one of the two X chromosomes in every female cell is inactivated during embryonic development. X-chromosome inactivation stops female cells from having twice as many X chromosome gene products as male cells. Hypermethylation often occurs, inhibiting gene expression, but hypomethylation can also occur, resulting in the opposite effect.

Another modification known as chromatin remodelling can alter how tightly the DNA is packaged in the chromosomes, relaxing the tightly packed chromosomes to allow the transcription factors which control gene expression access to the genes within.

Another type of epigenetic modification degrades (breaks down) the messenger RNA (mRNA) created when DNA is copied by the cell – a process called transcription. Here, non-coding RNA (a type of RNA that does not code for proteins) attaches to the mRNA and marks it for degradation.

Most epigenetic modifications are transient and reversible, allowing our cells to respond and adapt to changes in environment and behaviour. Although they happen on a molecular level, they can have a considerable impact on us and can also be influenced by external factors, such as diet and lifestyle.

Without epigenetics, you wouldn’t have developed from a fertilized egg to the multicellular organism you are today – and epigenetics will continue to impact on you, regulating specific genes in specific cells, in specific places and at specific times during your growth and development. 

Image slider – text version
The image displays methyl groups being added to the genome resulting in changes to gene expresson. Epigenetic modifications can change gene expression. Genes can be ‘switched on’ or ‘switched off’. Source: Genomics Education Programme, CC BY-NC 4.0
Epigenetic modifications can also relax the structure of the genome making it more accessible. Source: Genomics Education Programme, CC BY-NC 4.0

Concept in Action

Watch Epigenetics (3 mins) on YouTube for a short video that gives a succinct overview of Epigenetics and some of the factors that influence epigenetic modifications.

Video source: Centers for Disease Control and Prevention (CDC). (2022, October 20). Epigenetics [Video]. YouTube. https://youtu.be/ga4n-rGfdVY

Attribution & References

Except where otherwise noted, content on this page has been combined and adapted from:

License

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Precision Healthcare: Genomics-Informed Nursing Copyright © 2025 by Andrea Gretchev, RN, MN, CCNE is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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