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.
1 About 95 percent of the time, Down syndrome is caused by trisomy 21 â the child has three copies of chromosome 21 (instead of the usual two copies) in all cells. 2  This is caused by abnormal cell division during the development of the sperm cell or the egg cell.3  Mosaic Down syndrome.t's caused by a mistake in cell division during the development of the egg, sperm or embryo. Translocation Down syndrome is the only form of the disorder that can be passed from parent to child. However, only about 4 percent of children with Down syndrome have translocation.