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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. Most people have two copies of chromosome 21, while those with three copies of chromosome 21 ...
Down syndrome is caused in a minority (5% or less) of cases by a Robertsonian translocation of the chromosome 21 long arm onto the long arm of chromosome 14. [7] Chromosomal translocations between the sex chromosomes can also result in a number of genetic conditions, such as
In humans, when a Robertsonian translocation joins the long arm of chromosome 21 with the long arm of chromosomes 14 or 15, the heterozygous carrier is phenotypically normal because there are two copies of all major chromosome arms and hence two copies of all essential genes.
Notice the three copies of 21q (two chromosomes 21 and the long arm of chromosome 21 fused to the short arm of a chromosome 14). The extra chromosome 21 material that causes Down syndrome may be due to a Robertsonian translocation. The long arm of chromosome 21 is attached to the long arm of another chromosome, often chromosome 14 [46,XX,t(14 ...
Long arm; A chromosome is a ... In Down syndrome, there are three copies of chromosome 21. ... Edwards syndrome, or trisomy-18, the second most common trisomy. [53]
CM000680 ( FASTA) Chromosome 18 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 18 spans about 80 million base pairs (the building material of DNA) and represents about 2.5 percent of the total DNA in cells .
Specialty. Medical genetics. Distal 18q- is a genetic condition caused by a deletion of genetic material within one of the two copies of chromosome 18. [1] The deletion involves the distal section of 18q and typically extends to the tip of the long arm of chromosome 18. [2]
The largest regions on each chromosome are the short arm p and the long arm q, separated by a narrow region near the center called the centromere. Other specific regions have also been defined, some of which are similarly found on every chromosome, while others are only present in certain chromosomes. Named regions include: Arms (p and q ...