So we have something called the locus, we have something called a gene and something called an allele. And before we discuss what the difference is between these three different words and how they're related to one another, let's recall what a chromosome is. So, inside the nuclei of cells of different types of organisms, we have DNA molecules. Now, the problem is, if we take any single DNA molecule and we stretch it out like so, it will actually be quite long. So let's suppose that this is the nucleus of our cell and this is the actual DNA molecule. So notice it's much longer than the size of the nucleus itself.