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.
Trisomy 21â More than 90% of Down syndrome cases are caused by trisomy 21. An extra chromosome (chromosome 21) originates in the development of either the sperm or the egg. When the egg and the sperm unite to form the fertilized egg, three (rather than two) chromosomes 21 are present.
There are three chromosomal patterns that result in Down syndrome: Trisomy 21 (nondisjunction) is caused by a faulty cell division that results in the baby having three #21 chromosomes instead of two. Prior to or at conception, a pair of #21 chromosomes in either the egg or the sperm fails to separate properly.