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 caused by the presence of an extra 21st  chromosome. Instead of the typical 2 copies, a person with DS will  have 3 copies (known as a trisomy).   Down â¦ syndrome is not a mutation, but is usually an inherited  condition due to the extra genetic material in one of the parents'  egg or sperm, whether by Nondisjunction or by Translocation.