Down syndrome is a genetic disorder that occurs when an extra or partial copy of chromosome 21 is present. This genetic disorder was selected due to its popularity and prevalence of events. I find Down syndrome intriguing considering how a small defect in the way chromosomes separate can cause a multitude of symptoms, including, but not limited to, mental retardation and facial deformities. It's a disorder that many have heard of, but don't fully understand, which is why this genetic disorder irritates me. Rarely inherited, Down syndrome is caused by three types of chromosomal abnormalities: trisomy 21, mosaic Down syndrome, and translocation Down syndrome. The most common variant, Trisomy 21, occurs in about 95% of cases. According to “Down syndrome”, this common variation is caused by “an error during the formation of the egg or sperm” and causes “one of the two to have an extra chromosome”. After the sperm and the egg, the cells produced will have three copies of chromosome 21. Furthermore, Mosaic Down syndrome, which represents 3% of cases, causes some cells to be affected by three copies of chromosome 21, while others they are not affected. Finally, translocation Down syndrome occurs when “an extra part or entire extra chromosome 21 is present, but it is attached or “trans-located” to a different chromosome rather than being a separate chromosome 21” (“Facts about Down syndrome"). In this case, only an “unbalanced” translocation, in which genetic material is lost or acquired, can cause Down syndrome. Down syndrome remains the most widespread genetic disease in humans. According to the National Down Syndrome Society, it affects approximately 1 in 691 newborns and more than 400,000 individuals... middle of paper... with an increased risk of heart defects, vision and hearing problems, blood disorders and digestive problems . Nearly 50% of children with this disorder have congenital heart disease. This can lead to high blood pressure in the lungs, a weakening of the heart's ability to pump blood, and a reduction in oxygen in the bloodstream. Additionally, more than 60 percent of children with Down syndrome have vision problems, such as cataracts, that may be present at birth. Similarly, hearing loss affects approximately 70-75% of children due to a condition called “Diffuse Otitis Media,” which causes fluid to build up inside the middle ear. Finally, children with Down syndrome are 10 to 15 times more likely to develop leukemia than other children. Overall, Down syndrome can cause many harmful physical and mental disabilities and can also lead to other disorders.