But if we examine the carriotype of an individual that has trisomy 21, let's suppose the individual is a male individual. This is what we're going to see. So notice, every single one of these homologous pairs of chromosomes consists of two individual chromosomes, except chromosome pair 21. So in an individual, in a male individual that has trisomy 21, they have an extra additional copy of chromosome 21. So we have not two, but three of these individual chromosome 21. And so that's why this condition is known as trisomy 21.