I. Introduction. 1  The petroleum industry began with the successful drilling of the first commercial oil well in 1859, and the opening of the first refinery two years later to process the crude into kerosene.
The cause of Down syndrome is one of three types of abnormal cell division involving chromosome 21. All three abnormalities result in extra genetic material from chromosome 21, which is responsible for the characteristic features and developmental problems of Down syndrome.
Down Syndrome Causes and Symptoms. Down syndrome is a genetic disorder in which, most often, a third copy of chromosome 21 is present in cells because of an abnormal cell division when the egg and sperm first meet.