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.
A century after Down syndrome was first described, scientists discovered that the root cause of this disorder is a condition called trisomy 21. century after Down syndrome was first described, scientists discovered that the root cause of this disorder is a condition called trisomy 21.