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The ontological problem of defining DNA in secondary school biology: How I do it in Year 7

Updated: Aug 18, 2020

How should we define DNA (or in some cases, the nucleus) in secondary school? Since beginning teaching biology I have seen such things as:


  • The DNA/nucleus is the brain of the cell

  • The DNA/nucleus is the control centre of the cell

  • The DNA/genes are the blueprint for the body

  • The DNA/genes are the instructions for the body


And later in secondary education:

  • A gene codes for a trait / characteristic


All of which are poor metaphors leading to misconceptions. If we consider the value of these metaphors in terms of match (how well they describe the real thing), and range (how far they can take student understanding in education before it needs to be modified), then all rate poorly.


Let's look at them in more detail.

  • The DNA/nucleus is the brain of the cell

  • The DNA/nucleus is the control centre of the cell


These two metaphors invite the student to believe that 1. a single cell can think, 2. that there is an innate feeling of purpose and direction, and 3. that a cell somehow 'knows' about its parts, and can exert some sort of direct control over them. All these points are major obstacles for understanding how cells differ to inanimate matter. Cells are dynamic systems that emerge from countless interactions of molecules that encounter each other, often due to simple Brownian motion. The control and homeostasis of the cell lies not so clearly in the genetic material, but in feedback loops involving both the cytoplasm and genetic material, plus interactions with the environment. In this case, the genetic material plays a role in these interactions, but not the role, in the cell's state.


  • The DNA/genes are the blueprint for the body

  • The DNA/genes are the instructions for the body


These two anthropomorphic metaphors invite the student to believe in a design element to biology. Both blueprints and instructions are artifacts, which are designed to be followed for a purpose. The reading of blueprints and instructions invites a student to believe that a cell somehow has the ability of interpretation and knowledge of the bigger picture. The design of blueprints and instructions can lead a student towards believing in Intelligent Design rather than forming an understanding of evolution.


Furthermore, they liken the organism to a machine despite them differing in many aspects. Biological systems reproduce themselves and are flexibly robust with the ability to repair or compensate, through other processes, for any problems a system may incur.


  • A gene codes for a trait / characteristic


This final example metaphor, as with the previous two, encourage the student

to think with a genetically deterministic philosophy. Such erroneous outlooks on biology often shore up the equally fallacious social arguments of racists. Genes do not code for a trait, but for a protein or an RNA. It is the complex interactions of gene products and gene expression with the environment that produce the phenotype. Evo-devo, and phenotypic plasticity both show the crucial importance of environment on phenotype such that it is not a case of the old nature vs nurture dichotomy, but phenotype resulting from many interactions between genes and their products, and the environment. Dominant and recessive alleles, especially taught in the form of hereditary diseases, represent rare examples of simplicity compared to the totality phenotype causes.


So how should we define DNA to our secondary students, and what metaphors may be useful? Personally I think big ideas in biology transcend all topics and should be presented in every topic. I have written about this here. Therefore, our youngest secondary students should be introduced to the ideas of DNA during their first biology topic: Cells to Systems. Here I want to build a sound foundation for us to build upon over several years, but to also avoid unnecessary detail that may too abstract and confusing at this point in their biology education.


Ingo Brigandt suggests we should avoid all metaphors of machines and information in biology, but personally I like the word information as it has excellent match and range. If there are problems with it building misconceptions with a design principle, then we can attend to it, just as we may discuss problems with scientific models.


The next problem is to say what the information is that DNA contains. To evade forming ideas of genetic determinism we need to avoid anything that insinuates that the information pertains to the individual, as if we could read DNA and 'know' how that person will be. There are limits to the influence of DNA in a multicellular organism and I think it would be best, in the context of early secondary school biology, to suggest that its boundaries are the single cell; complexities of niche construction and Dawkins' extended phenotype are details that are beyond this stage of biology education.


Here's how I am currently teaching it to my Year 7 students.


During our first biology lesson I introduce unicellular organisms, using fantastic videos to see how they move and interact. Here I have to tackle the question: Do cells think? If I just say that they don't, I leave a void in which students may add their own ideas of how cells function. And so, immediately I must tackle the issue of DNA. Ensuring that I am always representing the interaction of environment with genetic material I use the following metaphor:





Images by Christian Moore Anderson


The issue with the metaphor containing a machine is problematic. Its virtues are that students understand quickly how a cell may function without the ability to think. To avoid further problems, just like with models, I proceed to question students about how good a metaphor it is. Do computers reproduce? Do they repair themselves? And most importantly, Were they designed? Etc.


The definition I give at this stage is:

DNA provides information to build a cell.


The next step is to understand how a multicellular organism can form if DNA only provides information for cells. This is tackled during the next lesson that looks at the organisation of multicellular organisms using the following image.




Here, again, the wording is important, I have chosen the word interacting carefully, and I have tried to make clear the influence of the environment.


In summary I see this as representing three things that I can show my Year 7 students:

  1. DNA provides information to build the cell, but the organism is ultimately formed through

  2. Interactions between cells

  3. Interactions between the cells and the environment.



Christian Moore Anderson

@CMooreAnderson (follow me on twitter)

Other posts you may enjoy:

Inheritance via 'Nature and Nurture'? It's time to change perspectives

Why physics & chemistry must precede biology in Year 7

The knowledge curriculum in biology: How retrieval practice and knowledge organizers may distort it






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