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22q11.2 deletion syndrome: Most people with 22q11.2 deletion syndrome are missing about 3 million base pairs on one copy of chromosome 22 in each cell. The deletion occurs near the middle of the chromosome at a location designated as q11.2. This region contains about 30 genes, but many of these genes have not been well characterized.
The shorter arm of a chromosome is termed the p arm or p-arm, while the longer arm is the q arm or q-arm. The chromosomal locus of a typical gene, for example, might be written 3p22.1, where: [citation needed] 3 = chromosome 3; p = p-arm; 22 = region 2, band 2 (read as "two, two", not "twenty-two") 1 = sub-band 1
The formations of nucleoli takes place around the NOR region. The secondary constriction also contains the genes for rRNA synthesis (18S rRNA, 5.8S rRNA, and 28S rRNA). Genes for 5S rRNA are present on chromosome 1. Due to secondary constriction, a knob-like structure is formed at the end called a satellite chromosome (SAT chromosome).
The C22orf25 gene is located on the long arm (q) of chromosome 22 in region 1, band 1, and sub-band 2 (22q11.21) starting at 20,008,631 base pairs and ending at 20,053,447 base pairs. [8]
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. [1] 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 ...
In humans, chromosomes Y and 22 have the greatest proportion of SDs: 50.4% and 11.9% respectively. [2] SRGAP2 is an SD. Misalignment of LCRs during non-allelic homologous recombination (NAHR) [ 3 ] is an important mechanism underlying the chromosomal microdeletion disorders as well as their reciprocal duplication partners. [ 4 ]
These microduplications likely represent the predicted reciprocal rearrangements to the microdeletions characterized in the 22q11.2 region. [2] Smaller microduplications may occur within this highly dynamic with frequent rearrangements using alternative low-copy repeats as recombination substrates within and distal to the DiGeorge syndrome region.
Various deletions affect the terminal region of the long arm of chromosome 22 (the paternal chromosome in 75% of cases, [citation needed]) from 22q13.3 to 22qter. Although the deletion is most typically a result of a de novo mutation, there is an inherited form resulting from familial chromosomal translocations involving the 22 chromosome.