Down syndrome is an abnormality of the chromosomes and not genic in origin .This occurs in one of every two thousand newborns. People do not "carry" this and the child is born with three rather than two chromosomes numbered 21. The mother and father of the child are normal except in the rare case of a woman with Down syndrome who gives birth to a child; the copying or replication error occurs either in the germ cell or in the initial cell division of the embryo.
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In the US, there are currently almost 500,000 people with Down Syndrome.
http://www.ds-health.com/risk.htm
Down syndrome is one of the most common genetic disorders, occurring in approximately 1 in 700 live births. However, other genetic diseases such as cystic fibrosis and sickle cell anemia have different frequencies depending on the population and genetic factors involved.
1 out of every 691 live births
0-9 purcent
For the United States, estimated as the fraction of people in the population with the syndrome, ~1/5500.
1 in every 1,000 babies that is born. 1 is the Down syndrome and 1,000 is the people that dont.
There are approximately7,222,222 people with down syndrome in the world ( if you compare the stat 1 in every 800-1000 births to the world's population of 6.5 billion).
down syndrome
Disorders, such as Down's Syndrome, are caused by nondisjunction.
Down syndrome