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
2018年3月8日 · About 95 percent of the time, Down syndrome is caused by trisomy 21 — the person has three copies of chromosome 21, instead of the usual two copies, in all cells. This is caused by abnormal cell division during the development of the sperm cell or the egg cell.
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
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 | Birth Defects | CDC - Centers for Disease ...
2024年5月16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.
Trisomy 21 (Down Syndrome) - Children's Hospital of Philadelphia
Trisomy 21 is the most common chromosomal anomaly in humans, affecting about 5,000 babies born each year and more than 350,000 people in the United States. Also known as Down syndrome, trisomy 21 is a genetic condition caused by an extra chromosome.
Down Syndrome - StatPearls - NCBI Bookshelf
2023年8月8日 · Down syndrome (trisomy 21) is a genetic disorder caused by the presence of all or a portion of a third chromosome 21. Patients typically present with mild to moderate intellectual disability, growth retardation, and characteristic facial features.