What is Trisomy 21?
Trisomy 21 is when there are three copies of the 21st chromosome instead of the expected two. This results in what is commonly known as Down Syndrome. The terminology of Trisomy 21 and Down Syndrome is commonly used interchangeably however in a biological context, there is a difference. Trisomy 21 occurs at the level of cell division where the expected cellular replication processes results in an unexpected amount of chromosomes and the process of this occurrence is called nondisjunction.
There are three types of trisomies that results in Down Syndrome. They are: Trisomy 21 or free trisomy, Mosaicism, and Translocation or Robertsonian translocation. The processes of each of these types of Trisomy originate differently. Some trisomies originate from the egg, sperm or zygote. To have a full understanding of how this occurs, requires a review of Grade 10 biology (for our purposes, we will cover the basics and not go into extreme detail of cellular replication and embryotic development, doing so would be to explain major concepts presented in biology 101). Continue reading “Pathophysiology of Down Syndrome”