This apple was found in an orchard right here in Nova Scotia. And if you ask fruit growers anywhere, they’ll tell you that they see these kinds of colour patterns pop up from time to time.
The distinct red colour that covers one quarter of this apple is caused by a mutation in the apple’s DNA sequence – a mutation that came about naturally. Nature is not perfect: it understandably makes mistakes sometimes when copying the 500 million letters of DNA sequence during each round of the billions of cell divisions that take place during the growth of an apple. These copying mistakes are called mutations. They happen in us too – some of them may change your hair colour while others may cause cancer. The mutation that led to the unique colour pattern in this apple happened during an early stage of fruit development – likely when the apple was made up of only 4 cells.
In one of those cells, a mutation occurred in the gene responsible for colour. This mutated cell then underwent cell division to create daughter cells which then also divided, and this process continued and eventually led to one quarter of the apple containing cells that contain the mutation. We call this apple a mosaic – it contains two populations of cells with different genotypes. Nature does some strange and wonderful things, which become even more fascinating as we learn more about them. We might just sequence the DNA from the two different populations of cells in this apple and try find the mutation that causes the colour difference. Stay tuned to see what we find!