Planning the teaching of the topic genetics at molecular level

Under this topic genetics at molecular level, I was going to teach about DNA, genes, nucleotides, genetic information, chromosomes and RNA. From the literature review that I had done, I was now aware of the knowledge gaps that students exhibit after being taught about the various structures of genetics. These knowledge gaps are as described below:

 Many students would show a good general understanding that genes determine characteristics, however, the students would show a lack of a basic understanding of what a gene is (its basic function, where it is found and how it relates to other structures) (Lewis et al., 2000b).

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 Some students would show an awareness that genes contain or provide information. However they would lack an understanding of the nature of this information and how it is used (Lewis et al., 2000b).

 Students would have the idea that the structures chromosome, gene and DNA play a role in determining the characteristics of an organism. However, they would show confusion regarding the respective roles of each of these molecules (Wood- Robinson, Lewis, & Leach, 2000).

 It was also seen that many students showed a limited understanding of the structure of and relationship between chromosomes and genes (Lewis & Wood-Robinson, 2000).

The above findings which were confirmed by many other researchers (e.g.Marbach-Ad, 2001; Quinn et al., 2009) helped me to be clear on the content that I was going to teach and how I was going to structure it. The content that I was going to teach under this topic is summarised below.

The nature of DNA, genes, chromosomes, chromatin and genetic information, the functions of DNA and genes, the specific roles of chromatin and chromosomes and the relationships between the genetic structures (DNA, genes, chromatin and chromosomes).

According to researchers, the knowledge summarised above is crucial for an understanding of genetics or the inheritance process. Therefore, I wanted to make sure that I was going to cover the structure and function of each entity, the relationship between them and the

role of each in the inheritance process. During the planning, I found out that I could easily

explain what these structures are and the relationships among them. My knowledge of why we had all those different forms was however scanty. I could see that I was not able to explain why we had all those different genetic structures. I had never thought about it and had never explicitly taught about it. This was a gap in my own knowledge of teaching genetics that I had just discovered that I needed to fill. The challenge now was for me to get this information. The research literature that I had reviewed didn’t contain this information. The biology textbooks that I had read didn’t have this explicit information. So I decided that I would start from what I knew about DNA, chromatin and chromosomes and engage in metacognitive activity as described in section 2.6.1. In the previous years I had used the diagram shown in Figure 17 below to explain how chromosomes form from DNA.

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Figure 17: Levels of DNA packaging

I revisited this diagram and studied it carefully. I thought about the title of my slide ‘Levels of

DNA packaging’. I thought about the word packaging. I looked up the word in the dictionary.

According to the Cambridge Advanced Learner’s Dictionary, packaging is a noun which describes ‘the materials in which objects are wrapped before being sold’ p 907. From this definition of the word packaging, the whole diagram became very clear to me: The DNA is the object of interest which is being wrapped around some material (histone proteins). The packaging produces more compact structures from DNA called chromatin and then a chromosome. Thinking about the long threadlike structure of DNA, I postulated that the purpose of organising DNA into a chromosome is for conservation of space within the nucleus of a cell and for efficiency: efficiency of storage of the DNA material and efficiency during the events of mitosis and meiosis. When I came to this understanding, I was convinced that the use of the idea of packaging for space conservation, and for efficiency, would form the basis of a conceptual understanding of the relationship between DNA molecules and chromosomes. The next question that I then asked myself was how best I should teach that concept. I then decided to use an analogy of string; how it is packaged after it has been manufactured for ease of storage, transportation and distribution (see Figure 18 below). The loose string represents a DNA molecule and the ball of string represents a chromosome.

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Figure 18: String analogy

After this metacognitive activity, I felt that I was ready to teach my first lecture. To support my teaching, I prepared the following visual aids:

 Pieces of coloured string tied one after another to explain what genes are and how they are related to DNA (Figure 19). The explanation would be that the long string made up of different coloured sections represents the DNA molecule, the coloured sections represents different genes on the DNA and the folded string represents DNA with its genes compacted into a chromosome.

Figure 19: Pieces of coloured string tied together

 Models of DNA to recap on the structure of DNA (Figure 20). I was going to use the model to discuss how the structure of DNA is suited to its functions; explain what genetic information is and the relationship between DNA, genes and genetic information.

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Figure 20: Model of DNA

String rolled on paper and on balls of Formica to show how chromatin forms first and then coils into a chromosome (Figure 21)

Figure 21: Visual objects to show how DNA organizes into chromatin then a chromosome