Down Syndrome Essay

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“Down Syndrome” The most common chromosomal abnormality in humans is Down Syndrome. Down Syndrome is a chromosomal condition where instead of having two copies of chromosome 21, there are three copies of it; also known as trisomy 21. This extra copy of chromosome 21 causes mental retardation, certain facial features, and a delay in growth. The average IQ of children who are diagnosed with Down Syndrome is 50, which is about half of an average child’s IQ. Intellectual disability is the largest form of disability in Down Syndrome cases. Down Syndrome is named after John Langdon Down. Down was a British physician who first discovered the condition in 1866. The condition was unofficially described earlier in 1838 by Jean Etienne Dominique Esquirol and in 1844 by Edouard Seguin. In 1959, Down Syndrome was described as a trisomy 21 by Dr. Jerome Lejeune. Down Syndrome can either be identified in a baby at birth or in a prenatal screening. The Center for Disease Control estimates that one in every 691 babies in America has down syndrome, making it the most common genetic disorder in America. Around 400,000 Americans and around 6,000 babies have Down Syndrome. There are three types of Down Syndrome. The first one is Trisomy 21 or “no disjunction”. Trisomy 21 is an embryo with three copies of chromosome 21 instead of the regular two. At conception, the 21st chromosome in either the sperm or the egg fails to separate. As the embryo develops, every cell in the body is replicated with the extra chromosome 21. This type of Down syndrome accounts for 95% of cases. The second type of Down Syndrome is Mosaicism. Mosaicism is when not all of the cells are replicated with trisomy 21. When this happens, there is a mix of cells. Some will contain 46 total chromosomes and some will contain 47. Mosaicism accounts for about 1% of all cases of Drown Syndrome. Mosaicism doesn’t
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