Chromosome 5 is one of the 23 pairs ofchromosomes inhumans. People normally have two copies of this chromosome. Chromosome 5 spans about 182 millionbase pairs (the building blocks ofDNA) and represents almost 6% of the total DNA incells. Chromosome 5 is the 5th largest human chromosome, yet has one of the lowestgene densities. This is partially explained by numerous gene-poor regions that display a remarkable degree ofnon-coding andsyntenic conservation with non-mammalianvertebrates, suggesting they are functionally constrained.[4]
The following are some of the gene count estimates of human chromosome 5. Because researchers use different approaches togenome annotation their predictions of thenumber of genes on each chromosome varies (for technical details, seegene prediction). Among various projects, the collaborative consensus coding sequence project (CCDS) takes an extremely conservative strategy. So CCDS's gene number prediction represents a lower bound on the total number of human protein-coding genes.[6]
The following conditions are caused by changes in the structure or number of copies of chromosome 5:
Cri-du-chat syndrome is caused by a deletion of the end of the short (p) arm of chromosome 5. This chromosomal change is written as 5p-. The signs and symptoms of cri-du-chat syndrome are probably related to the loss of multiple genes in this region. Researchers have not identified all of these genes or determined how their loss leads to the features of the disorder. They have discovered, however, that a larger deletion tends to result in more severe mental retardation and developmental delays in people with cri-du-chat syndrome.[13][14][15]
Researchers have defined narrow regions of the short arm of chromosome 5 that are associated with particular features of cri-du-chat syndrome. A specific region designated 5p15.3 is associated with a cat-like cry, and a nearby region called 5p15.2 is associated with mental retardation,small head (microcephaly), and distinctive facial features.
Familial Adenomatous Polyposis is caused by a deletion of theAPC tumor suppressor gene on the long (q) arm of chromosome 5. This chromosomal change results in thousands of colonic polyps which gives the patient a 100% risk of colon cancer if total colectomy is not done.
Chromosome 5q deletion syndrome is caused by the deletion of the q arm (long arm) of chromosome 5. This deletion has been linked to several blood related disorders includingMyelodysplastic syndrome andErythroblastopenia. This is a different condition than Cri-du-chat which was mentioned above.
Other changes in the number or structure of chromosome 5 can have a variety of effects, including delayed growth and development, distinctive facial features, birth defects, and other medical problems. Changes to chromosome 5 include an extra segment of the short (p) or long (q) arm of the chromosome in each cell (partial trisomy 5p or 5q), a missing segment of the long arm of the chromosome in each cell (partial monosomy 5q), and a circular structure calledring chromosome 5. A ring chromosome occurs when both ends of a broken chromosome are reunited.
G-banding ideogram of human chromosome 5 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).
G-banding patterns of human chromosome 5 in three different resolutions (400,[16] 550[17] and 850[3]). Band length in this diagram is based on the ideograms from ISCN (2013).[18] This type of ideogram represents actual relative band length observed under a microscope at the different moments during themitotic process.[19]
G-bands of human chromosome 5 in resolution 850 bphs[20]
^For cytogenetic banding nomenclature, see articlelocus.
^abThese values (ISCN start/stop) are based on the length of bands/ideograms from the ISCN book, An International System for Human Cytogenetic Nomenclature (2013).Arbitrary unit.
^gpos: Region which is positively stained byG banding, generallyAT-rich and gene poor;gneg: Region which is negatively stained by G banding, generallyCG-rich and gene rich;acenCentromere.var: Variable region;stalk: Stalk.
