Down syndrome is a genetic disorder that occurs when an extra or partial copy of chromosome 21 is present. This genetic disease was selected due to its popularity and prevalence. I find Down syndrome intriguing given that a small defect in the way chromosomes separate can cause a host 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 gives me pause. Rarely hereditary, Down syndrome is caused by three types of chromosomal abnormalities: Trisomy 21, Mosaic Down Syndrome and Down translocation syndrome. The most common variant, Down syndrome, 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 results in “one or the other having an extra chromosome.” After the sperm and egg mate, the cells produced will have three copies of chromosome 21. In addition, Mosaic Down syndrome, which accounts for 3% of cases, leads to certain cells being affected with three copies of the chromosome 21, while others are not affected. Finally, Down translocation syndrome occurs when an “extra part or entire extra chromosome 21 is present, but it is attached or “translocated” 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 gained, can cause Down syndrome. Down syndrome remains the most common genetic disorder 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 problems and hearing, blood disorders and digestive problems. Nearly 50% of babies with this condition have congenital heart disease. This can lead to high blood pressure in the lungs, a weakened ability of the heart to pump blood, and reduced oxygen in the blood. Additionally, more than 60% of children with Down syndrome have vision problems, such as cataracts, which may be present at birth. Similarly, hearing loss affects approximately 70 to 75 percent of children due to a condition called "diffuse otitis media," which causes fluid to build up in 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 detrimental physical and mental disabilities, as well as other disorders..