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.
Â· just now. 1  Down syndrome is caused by a problem with a babyâs chromosomes that happens long before the baby is born. 2  Down syndrome is a chromosomal disorder where an extra copy of chromosome 21 is made, the term is called trisomy 21. 3  It is caused by trisomy, having 3 of the same chromosomes (chromosome 21) One usually have 2 of the same chromosomes, but down syndrome has 3. i a chromosomal disorder caused by the presence of all or part of an extra 21st chromosome. one extra chromosome.