Research has shown that a mother has a 1 in 800 chance of having a child with Down syndrome. The risk go up dramatically if mother is over 48 – now having a 1 in 9 chance of having a child with Down Syndrome. Down syndrome was first document by an English physician named John Down in the late 1880’s. Down syndrome is a congenital condition which causes mental retardation and a variety of other defects. It is by far the most widespread chromosomal abnormality found in any syndrome to date. This abnormality occurs when an extra chromosome appears on the 21st chromosomes, so instead of the normal two chromosomes now there are three.
Chromosomes are thread like structures that are made up of DNA matter and other proteins. These chromosomes are part of the basic structure of the cells and present in every cell in the body. It is these chromosomes that carry the genetic information needed for cells to develop. Human cells normally have 46 of these chromosomes which paired together in 23 sets. However, during the fertilization stage of an egg, sperm and the egg cells are created through a process called meiosis in which each pair of chromosomes split which causes the sister cell and the original cell each now to have 23 chromosomes. So during fertilization each egg cell and sperm cell contains only 23 chromosomes – at conception when the two cells combine and they now form the complete set of 46 chromosomes.
Soon after fertilization, the second method of cell division begins - the egg begins to grow and develops by dividing by mitosis into two identical new cells. As these cells duplicate, their genetic material is also duplicated so that each new cell receives the same chromosomal material as the original fertilized cell. Because all cells duplicate the genetic structure of the first fertilized egg, its genetic content determines the genetic make-up of the embryo.
During meiosis many abnormal events or mistakes can occur. These abnormal events or mistakes...