Teaching Evolution 2/5 – Mutations
Nobody understands mistakes like kids. Unless, of course, you mean the teachers who have to correct them. I find my students get very interested in the idea of mutation and starting from the media version – X-Men for example – we work towards a more accurate description, of a mistake that is made during the copying of genes in cell division. I find it useful to mention mutations in body cells and their causes (chemical triggers such as tar and benzene, viruses like HPV and nuclear radiation). With an articulate, curious class, this can turn into a lesson of its own!
With a new individual that has an altered gene compared to the parents, there are two possibilities. If in ‘non-coding’ or junk DNA, there will be absolutely no effect. (Variations in these sections are used for DNA fingerprinting, which students can learn about by doing a Nova Interactive.) If it is in ‘coding’ DNA, those sections that actually do something, then there are several possible outcomes:
- it makes exactly the same protein – no observable change
- it makes a similar protein that does effectively the same job
- it makes a protein which does the job slightly better or worse
- it doesn’t make a protein at all (and the organism can’t survive)
Most mutations that cause any effect at all, cause a negative effect. The example – explained better in the powerpoint linked below – is that if we change a random letter on a page of a book, it is unlikely to make the book better. These mutations are random, not deliberate. The chances of a mutation improving the functioning of a protein or cell is small, to say the least.
In my activity – Evolution In Other Words as ppt – students start with a word and ‘mutate’ it by changing one letter at a time. I’m playing with ways of making this more random, perhaps by using Scrabble tiles. The idea is that students will see not only that mutation can happen, but that after a few ‘generations’ it is hard to see relationships, both between ‘ancestor’ and ‘descendant’ words, and between ‘cousins’ – words which diverged by changing a different letter. Depending on how much of the powerpoint is used, students can also be prepared for concepts such as selection and speciation.
What’s interesting to me is that many surviving mutations will appear to be survival-neutral – they don’t make an organism better or worse at surviving. I often give the contrasting examples of fur colour and eye colour. Different colours of fur are clearly relevant for survival in the wild, but eye colour, as long as it is not linked to eyesight, shouldn’t matter. This is a nice way to introduce the concept that sometimes the advantages of a characteristic are difficult to observe, subtle or non-existent.
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