Down Syndrome

Down Syndrome is a condition caused by trisomy 21 due to nondisjunction in meiosis. As a result, instead of normal 46 chromosomes, an affected person will have 47 chromosomes. Nondisjunction of the chromosome number 21 normally occurs in the gamete of the ovum of the mother in her forties. Down syndrome also occurs due to an unusual chromosome structure but at a very small percentage. The similar phenotypic feature of people with Down Syndrome is that they have broad and flat heads and flattened noses. Affected people have lower intellectual capacity and defective health with a shortened life expectancy which is less than 50 years.