" Down based this unfortunate name on his notion that these children looked like people from Mongolia, who were thought then to have an arrested development (Mao 457)." The term was dropped from scientific use when this ethnic slur came under fire in the 1960s from Asian genetic researchers. Instead, the condition became known as "Down's syndrome.".
In the 1970s, an American modification of scientific terms changed it simply to "Down syndrome," due to the implication of ownership caused by the possessive apostrophe, even though it is still called "Down's" in Europe. During the first part of the twentieth century, the causes of DS were speculated over. Waardenberg and Bleyer were the first to consider that Down syndrome might be chromosomal in nature during the 1930's. However, it wasn't until 1959 that Jerome Lejeune and Patricia Jacobs, each of them working independently, first determined the cause to be triplication (trisomy) of the 21st chromosome. To understand the pathophyisology of Trisomy 21 you must first understand the basic structure of chromosomes. Chromosomes are thread-like structures composed of DNA and other proteins. They are present in every cell of the body and carry the genetic information needed for that cell to develop. Genes (which are units of information) are "encoded" in the DNA. "Human cells normally have 46 chromosomes, which can be arranged in 23 pairs. Of these 23, 22 are alike in males and females; these are called the "autosomes" (Finch 1995)." .
The 23rd pair of chromosomes is the sex chromosomes ('X' and 'Y'). Each member of a pair of chromosomes carries the same information, in that the same genes are in the same spots on the chromosome. However, deviations of that gene (alleles) may be present. (Example: the genetic information for eye color is a "gene;" the variations for blue, green, etc. are the alleles.) Human cells divide in two ways, the first being ordinary cell division (mitosis), by which the body grows (Yang 182).