Chromosome 22 is one of the 23 pairs of chromosomes in human cells. Humans normally have two copies of chromosome 22 in each cell, Chromosome 22 is the second smallest human chromosome, spanning about 49 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 pairs that make up this chromosome. Chromosome 22 was the first human chromosome to be fully sequenced, identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to genome annotation their predictions of the number of genes on each chromosome varies, in January 2017, two estimates differed by 33%, with one estimate giving 956 genes, and the other estimate giving 1,110 genes. Chromosome 22 was originally identified as the smallest chromosome, after extensive research, however, researchers concluded that chromosome 21 was smaller. The deletion occurs near the middle of the chromosome at a designated as q11.2. This region contains about 30 genes, but many of these genes have not been well characterized, a small percentage of affected individuals have shorter deletions in the same region. A loss of this gene does not appear to cause learning disabilities, other genes in the deleted region are also likely to contribute to the signs and symptoms of 22q11.2 deletion syndrome. Cat-eye syndrome is a rare disorder most often caused by a change called an inverted duplicated 22. A small extra chromosome is made up of material from chromosome 22 that has been abnormally duplicated. A rearrangement of genetic material between chromosomes 9 and 22 is associated with types of blood cancer. This chromosomal abnormality, which is called the Philadelphia chromosome, is found only in cancer cells. The Philadelphia chromosome has been identified in most cases of a slowly progressing form of cancer called chronic myeloid leukemia. It also has found in some cases of more rapidly progressing blood cancers. The presence of the Philadelphia chromosome can help predict how the cancer will progress, emanuel Syndrome is a translocation of chromosomes 11 and 22. Originally known as Supernumerary der Syndrome, it occurs when an individual has an extra chromosome composed of pieces of the 11th and this is based on a physiological mechanism and is not pathogenetic for leukemias or lymphomas. However, the rearrangement of several lambda variable subgenes can activate expression of an overlapping miRNA gene, the DNA sequence of human chromosome 22
Image: Human male karyotpe high resolution Chromosome 22
Image: Human chromosome 22 400 550 850 bphs
G-banding ideogram of human chromosome 22 in resolution 850 bphs. Band length in this diagram is proportional to base-pair length. This type of ideogram is generally used in genome browsers (e.g. Ensembl, UCSC Genome Browser).