So not all down syndrome cases are due to trisomy 21, although the majority are due to trisomy 21. About 4% of the individuals with down syndrome actually still have the normal number of chromosomes 46, but one of them is abnormal as a result of the process we call chromosomal translocation. So for example, let's suppose we have the following two normal pairs of chromosome. We have chromosome 14 and so this chromosome pair right here and chromosome pair 21. Now, what do we mean by chromosomal translocation? So what chromosomal translocation means is a segment of one chromosome.