History of Down Syndrome
In the 20th century people with down syndrome as well as those with other disabilities were still being institutionalized and often sterilized. in Germany 1940, Hitler implented the Akiton T-4 program, which refers to euthanize people with down syndrome and other disabilities.

1959 DR Jerome Lejune, a French physician made the discovery that down syndrome was the result of the chromosomal abnormality. His research helped him see that people with the disorder had 47 chromosomes, whereas people without the disorder had 46 chromosomes. After that, he discovers that chromosome number 21 contained an extra partial or complete chromosome in these mongoloids, because of that the term Trisomy 21 was born.
trisomy 21 karyotype
trisomy 21 karyotype

Human cells divide in two ways. The first is ordinary cell division ("mitosis"), by which the body grows. In this method, one cell becomes two cells which have the exact same number and type of chromosomes as the parent cell. The second method of cell division occurs in the ovaries and testicles ("meiosis") and consists of one cell splitting into two, with the resulting cells having half the number of chromosomes of the parent cell. So, normal eggs and sperm cells only have 23 chromosomes instead of 46.

Many errors can occur during cell division. In meiosis, the pairs of chromosomes are supposed to split up and go to different spots in the dividing cell; this event is called "disjunction." However, occasionally one pair doesn't divide, and the whole pair goes to one spot. This means that in the resulting cells, one will have 24 chromosomes and the other will have 22 chromosomes. This accident is called "nondisjunction." If a sperm or egg with an abnormal number of chromosomes merges with a normal mate, the resulting fertilized egg will have an abnormal number of chromosomes. In Down syndrome, 95% of all cases are caused by this event: one cell has two 21st chromosomes instead of one, so the resulting fertilized egg has three 21st chromosomes. Hence the scientific name, trisomy 21. Recent research has shown that in these cases, approximately 90% of the abnormal cells are the eggs. The cause of the nondisjunction error isn't known, but there is definitely connection with maternal age. Research is currently aimed at trying to determine the cause and timing of the nondisjunction event

People that receive the disorder are the ones that have 47 chromosomes. people with the disorder are living a full and happy life, but may need a little help with learning things