Chromosome 21 - Wikipedia
Chromosome 21 is one of the 23 pairs of chromosomes in humans. Chromosome 21 is both the smallest human autosome and chromosome, [4] with 46.7 million base pairs (the building material of DNA) representing about 1.5 percent of the total DNA in cells.
Down syndrome - Symptoms and causes - Mayo Clinic
2024年11月12日 · Down syndrome is a genetic condition caused when an unusual cell division results in an extra full or partial copy of chromosome 21. This extra genetic material causes the developmental changes and physical features of Down syndrome. The term "syndrome" refers to a set of symptoms that tend to happen together.
Chromosome 21 - MedlinePlus
Chromosome 21 is the smallest human chromosome, spanning about 48 million base pairs (the building blocks of DNA) and representing 1.5 to 2 percent of the total DNA in cells. Learn about health implications of genetic changes.
Down Syndrome: Symptoms & Causes - Cleveland Clinic
2023年1月31日 · Down syndrome is a genetic condition where a person is born with an extra copy of chromosome 21. This means that they have a total of 47 chromosomes instead of 46. This can affect how their brain and body develop. People diagnosed with Down syndrome have happy and healthy lives with supportive care. Down syndrome can affect how your child develops.
Down syndrome - Wikipedia
Down syndrome or Down's syndrome, [12] also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. [3] . It is usually associated with developmental delays, mild to moderate intellectual disability, …
Down Syndrome | Birth Defects | CDC - Centers for Disease …
2024年10月28日 · Down syndrome is a condition in which a person has an extra copy of chromosome 21. Chromosomes are small "packages" of genes in the body's cells, which determine how the body forms and functions. When babies are growing, the extra chromosome changes how their body and brain develop.
What causes Down syndrome? | NICHD - NICHD - Eunice …
2012年6月11日 · Down syndrome is caused by a random error in cell division that results in the presence of an extra copy of chromosome 21. The type of error is called nondisjunction. Usually when one cell divides in two, pairs of chromosomes are split so that one of the pair goes to one cell and the other from the pair goes to the other cell.
Down Syndrome: Trisomy 21, Causes, 6 Symptoms, 2 Tests ... - MedicineNet
Down syndrome (trisomy 21) is most commonly caused by chromosome replication errors in which there are three copies of chromosome 21 instead of two. A baby born with Down syndrome may have symptoms and signs such as unusual facial features, low IQ, and difficulty learning to walk and crawl.
Down Syndrome (Trisomy 21) - Pediatrics - The Merck Manuals
Down syndrome is an abnormality of chromosome 21 that can cause intellectual disability, microcephaly, short stature, and characteristic facies. Diagnosis is suggested by physical anomalies and abnormal development and confirmed by cytogenetic analysis. Management depends on specific manifestations and anomalies.
Trisomy 21: What You Need to Know - Massachusetts General Hospital
Trisomy 21 (more commonly known as Down syndrome) is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. Learn how it happens. What is trisomy 21? Trisomy 21 happens when an extra copy of chromosome 21 is present in all cells of the body.
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