Down Syndrome : Genetic Disorder

1293 WordsNov 11, 20146 Pages
Down syndrome is a genetic disorder that begins to develop at the cellular level after conception. All the cells in the human body contain a center, called a nucleus, in which genetic code of each human being is stored. This genetic material, known as genes, carries the codes responsible for all our inherited characteristics from the mother and the father. Genes are grouped along rod-like structures called chromosomes. The nucleus of each cell normally contains 23 pairs of chromosomes, half of which come from each parent. In Down syndrome, however, the cells usually contain not 46, but 47 chromosomes. The extra chromosome being a number 21. This excess genetic material, in the form of additional genes along the 21st chromosome, results in Down syndrome. Ninety-five percent of all cases of Down syndrome occur because there are three copies of the 21st chromosome; it is often referred to as "trisomy 21." Chromosomes are studied by examining blood or tissue cells. Individual chromosomes are identified, stained and numbered from largest to smallest. The visual display of the chromosomes is known as a “karyotype”. (Karyotype is the analysis of counting the chromosomes in each cell) Down syndrome a mistake in the cell division called non-disjunction. Two other minor types of chromosomal abnormalities, “mosaicism” and “translocation”, are also causes of Down syndrome. Mosaicism is the state of being composed of cells of two genetically different types. Translocation is the exchange
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