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.
Down syndrome is usually caused by a condition known as Trisomy 21, which means that a person has three copies of Chromosome 21, rather than the usual two copies. An extra chr â¦ omosome is added. The normal amount is 46, but people with Down syndrome have 47.