A great way to extend your more able students when studying DNA is to take a look at what happens when the DNA code goes wrong and mutations occur. Why not share with them this story of an extraordinary cat.
Meet Yoda – the cat with a mutation
Yoda the Four-Eared Cat
Yoda the cat has an extra pair of ears caused by a mutation. When you hear the word ‘mutation’ you may think of superheroes who got their special powers because of being exposed to radiation. Although it is true that radiation can cause mutations; in real-life the effects of mutations are much less exciting. They can sometimes cause differences in characteristics, like in Yoda’s case, or they may cause an illness. Sometimes they make no difference to the organism at all.
A mutation is a change in the order of the bases in the strand of DNA. DNA is a code for all our characteristics. The code is actually made up of a sequence of bases (the ‘rungs’ of the DNA double helix) which we give the letters A, T, G and C. The order of the bases in a gene is what determines the characteristic it codes for. For example, if we look at the gene for eye colour, the blue eye version will have a different order of bases to the brown eye version.
Mutations can be caused by chemicals, radiation or a mistake when the DNA copies itself. A base may change into a different one or a section of DNA might get deleted or added. If the mutated region of DNA is in a gene this may result in a change in the characteristic the gene codes for.
Sometimes a mutation might make an organism better suited to its environment. An example is a mutation in a bacterial cell which means it can no longer be killed by antibiotics. This bacteria will survive and its offspring will inherit the mutation. This is the basis of how evolution by natural selection works.
Some questions for your students to think about:
Why don’t mutations always lead to a change in the characteristics of an organism?
The mutation must happen in a gene (many regions of DNA are not in genes – they do not code for proteins). Also, the mutation must result in a change in the protein being made. As amino acids are coded for by several different codons (triplet bases) a change in the code doesn’t always results in a change in the amino acid sequence of the protein.
How could we find out what the mutation is that causes Yoda’s extra pair of ears?
You could find out Yoda’s genome (the order of the bases in his DNA) and compare this to a cat without four ears to see where the changes are.
UV light from the sun can damage DNA and cause mutations. What illness can this lead to?
Skin cancer. The mutation causes the skin cells to divide uncontrollably, forming a lump of cells called a tumour.
Genetic mutation causing the condition Hemophilia
Your students can watch a video of Yoda:
Not the whole video needs to be shown – just a region with the cat (0:46-1:09)
Extension Work
To further extend their knowledge about the structure of DNA your students will also enjoy this free science resource on DNA and watching this video on explaining DNA.