Now, the reason that this exists is a result of nondisjunction that can take place either in meiosis one or meiosis two, more specifically in anaphase one or anaphase two or of meiosis. So to see exactly what we mean by that, let's take a look at the following diagram that describes nondisjunction taking place in anaphase II of meiosis. So let's suppose we have a normal female individual, and that normal female individual produces Xcel. So this is the precursor cell that eventually gives rise to four X cells. Now, because we're dealing with a normal female individual, we have two X chromosomes, x chromosome number one and X chromosome number two. Now, during interface, before meiosis actually takes place, each one of these X chromosomes is actually replicated.