Down Syndrome: Trisomy 21

Topics: Down syndrome, Aneuploidy, Cytogenetics Pages: 4 (1227 words) Published: February 2, 2014
Abstract
Down syndrome, also known as trisomy 21, is the most common chromosome abnormality in humans and it occurs in all races. Approximately 1 of every 691 babies born in the United States each year is born with this genetic condition. Because people with Down syndrome have extra copies of genes on chromosome 21, the course of normal development is disrupted and this leads to the distinctive physical characteristics and other health issues that are associated with this syndrome. With appropriate medical care and supportive therapies, individuals with Down syndrome can lead happy and fulfilling lives.

Down Syndrome: Trisomy 21
Typically, every person is born with 23 pairs of chromosomes, for a total of 46 chromosomes. Upon conception, a fetus begins to develop when it receives 23 chromosomes from both the mother’s egg and from the father’s sperm. In individuals born with Down syndrome (trisomy 21), an error occurs during meiosis that causes an extra chromosome on every cell of their body. The extra 47th chromosome in Down syndrome is located in the 21st position and it may be either a full or a partial extra copy. The exact cause of errors that result in the extra chromosome in trisomy 21 is not well understood, however, studies have shown that 95% of trisomy 21 is maternal in origin. The most significant risk factor that is known to increase the risk of having a child born with Down syndrome is the age of the mother. Down syndrome is a relatively common disease. In fact, it is the most common chromosome abnormality in Homo sapiens and it occurs in all races. According to the Centers for Disease Control and Prevention, approximately 1 of every 691 babies born in the United States each year is born with Down syndrome and approximately 95% of those cases are trisomy 21. In total, there are over 400,000 people in the US living with Down syndrome. Because people with Down syndrome have extra copies of genes on chromosome 21, the course of...

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