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.
Like Patau syndrome, Down syndrome is caused by having an extra copy of a certain chromosome. Individuals with Down syndrome usually have an extra copy of chromosome 21. Thus, Down syndrome is commonly called trisomy 21. Perhaps not surprisingly, the cause of the trisomy in both Patau and Down syndromes is similar. A phenomenon called nondisjunction is responsible for most cases of trisomy 13 and 21.