Now, to see exactly what we mean by that, let's take a look at the following diagram. So this is one example of how tricemy 21 can actually take place, can actually occur. So let's suppose we're dealing with a normal female individual. So since we're dealing with a normal female individual, that means each one of these pairs of chromosomes will consist of two, and that includes chromosome pair 21. And because we're focusing on trisomy 21 in this diagram, I've only drawn this chromosome pair 21. So we have a normal female individual.