Down Syndrome

An extra copy of chromosome 21 is what causes down syndrome. In a normal human complement, there are 23 pairs of chromosomes. But what is down syndrome and what causes this to happen? Down syndrome is a genetic condition in which a person has 47 chromosomes instead of 46, which is the normal amount. This is also a related to trisomy 21. Trisomy 21 is when there are three number 21 chromosomes, making 47 chromosomes in total. It is the most common chromosome number abnormality and the most common serious birth defect in the U.S. It affects about one out of every seven hundred children. Some of the characteristics of a person with down syndrome possess a round face, a skin fold at the inner corner of the eye, a flattened nose bridge, and small, irregular teeth. They're also short and have heart defects. As well as susceptibility to respiratory infections, leukemia, and Alzheimer's disease. Generally, people with down syndrome have a shorter life span than others. The older a woman is when she has a baby, the higher the percentage is for her to have a child with this chromosome defect. Less than .05% in women under the age of 30, 1% for mothers at age 40, and the percentage is even higher for older mothers.

http://anthro.palomar.edu/abnormal/images/Down_Syndrome_Karyotype.jpg