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Chromosome 22 is the second smallest human chromosome, spanning about 51 million DNA base pairs and representing between 1.5 and 2% of the total DNA in cells. In 1999, researchers working on the Human Genome Project announced they had determined the sequence of base pairs that make up this chromosome.
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).
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.
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 ]
Which are essentially instructions for everything from development to day-to-day survival, and these genes are spread out across 23 pairs of chromosomes. 22q11.2 is like an address, so 22 stands for chromosome 22, with q designating the long arm of the chromosome, then it’s on region 1, band 1, and sub-band 2.
PAR1 comprises 2.6 Mbp of the short-arm tips of both X and Y chromosomes in humans and great apes (X and Y are 154 Mbp and 62 Mbp in total). PAR2 is at the tips of the long arms, spanning 320 kbp. [5] The monotremes, including the platypus and echidna, have a multiple sex chromosome system, and consequently have 8 pseudoautosomal regions. [6]
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.