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. Down Syndrome is a leading cause of mental retardation. Down Syndrome is a genetic condition caused by an extra chromosome. Students with Down Syndrome have distinct physical features.tudents with Down Syndrome exhibit a wide range of behaviors and abilities, however, most have some degree of mental retardation. Language and motor development are usually slow, and speech articulation may be poor.