Trisomy 21: Down Syndrome

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This person has three copies of one of their chromosomes instead of two. This is known as trisomy. The chromosome that is affected in this individual is chromosome 21. Although chromosome 21 is the smallest one humans have, it can cause a lot of problems if it is altered. This includes several kinds of cancers, such as a type of leukemia. It can also effect mental development and growth. Since this person has three chromosome 21's instead of two, this means that they have Down syndrome. It was identified as being a chromosome 21 trisomy in 1959 by Dr. Jérôme Lejeune. Down syndrome is named after John Langdon Down, a british physician who wrote about the syndrome in 1866. It is also the most common chromosome abnormality in humans. In the United States alone, about around 1 in 700 children are born with it. It is unknown why it occurs. It is, however, known what increases the probability of it happening. The risk of it occurring increases as the mother ages. Women who are over the age of thirty-five have a much higher chance of producing a child with it. When somebody has this gene...

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