Now, virtually all chromosomal abnormalities that arise in humans are syndromes and that's because they cause multiple symptoms, both physical as well as mental symptoms. Now, the most common type of chromosomal abnormality in humans is down syndrome syndrome. And this will be the focus of this lecture. So we're going to see that there are two forms of down syndrome. The first form, the more common form, is trisomy 21. And the other form, the less common form, is translocation.