The X chromosome is the larger of the pair of chromosomes that determine sex in mammals. It is present in two copies in females, while one copy pairs with the sex determining Y chromosome in males.
Keywords: X chromosome
Chromosome X: General Features
Matthew J Wakefield, The Australian National University, Canberra, Australia
Jennifer AM Graves, The Australian National University, Canberra, Australia
Published online: January 2006
DOI: 10.1038/npg.els.0005794
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Figure 1. Hemophilia pedigree of Queen Victoria's offspring. Females are represented by circles and males by squares. Affected individuals are represented by filled squares. Carrier females are represented by a smaller filled circle. Note how the disease is apparent in males of only every second generation, the classic skipping of generations that is associated with X-linked recessive disease.
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Figure 2. Metaphase chromosome spread from a patient with fragile X. Note the constriction on the long arm of the X chromosome (indicated by the arrow and enlarged in inset). (Picture courtesy Professor C. M. Disteche, Department of Pathology, University of Washington, Seattle, WA, USA.)
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| Further Reading | |
| Graves JAM (1995) The origin and function of the mammalian Y chromosome and Y-borne genes – an evolving understanding. BioEssays 17: 311–320. | |
| Graves JAM and Delbridge ML (2001) The X – a smart and sexy chromosome. BioEssays 23: 1091–1094. | |
| Lubs H, Chiurazzi P, Arena J, Tranebjaerg L and Neri G (1999) XLMR genes: update 1998. American Journal of Medical Genetics 83: 237–247. | |
| Nathans J (1999) The evolution and physiology of human color vision: insights from molecular genetic studies of visual pigments. Neuron 24: 299–312. | |
| book Ohno S (1967) Sex Chromosomes and sex Linked Genes Berlin: Springer. | |
| Web Links | |
| ePath National Hemophilia Foundation http://www.hemophilia.org/ | |
| ePath IRSA: International Rett Syndrome Association http://www.rettsyndrome.org/ | |
| ePath The National Fragile X Foundation http://www.fragileX.org/ | |
| ePath Androgen receptor (dihydrotestosterone receptor; testicular feminization; spinal and bulbar muscular atrophy; Kennedy disease) (AR); Locus ID: 367 LocusLink: http://www.ncbi.nlm.nih.gov/LocusLink/LocRpt.cgi?l=367 | |
| ePath Coagulation factor VIII, procoagulant component (hemophilia A) (F8); Locus ID: 2157 LocusLink: http://www.ncbi.nlm.nih.gov/LocusLink/LocRpt.cgi?l=2157 | |
| ePath Fragile X mental retardation 1 (FMR1); Locus ID: 2332 LocusLink: http://www.ncbi.nlm.nih.gov/LocusLink/LocRpt.cgi?l=2332 | |
| ePath Methyl CpG binding protein 2 (Rett syndrome) (MECP2); Locus ID: 4204 LocusLink: http://www.ncbi.nlm.nih.gov/LocusLink/LocRpt.cgi?l=4204 | |
| ePath Sex determining region Y (SRY); Locus ID: 6736 LocusLink: http://www.ncbi.nlm.nih.gov/LocusLink/LocRpt.cgi?l=6736 | |
| ePath X (inactive)-specific transcript (XIST); Locus ID: 7503 LocusLink: http://www.ncbi.nlm.nih.gov/LocusLink/LocRpt.cgi?l=7503 | |
| ePath Androgen receptor (dihydrotestosterone receptor; testicular feminization; spinal and bulbar muscular atrophy; Kennedy disease) (AR); MIM number: 313700 OMIM: http://www.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?313700 | |
| ePath Coagulation factor VIII, procoagulant component (hemophilia A) (F8); MIM number: 306700 OMIM: http://www.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?306700 | |
| ePath Fragile X mental retardation 1 (FMR1); MIM number: 309550 OMIM: http://www.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?309550 | |
| ePath Methyl CpG binding protein 2 (Rett syndrome) (MECP2); MIM number: 300005 OMIM: http://www.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?300005 | |
| ePath Sex determining region Y (SRY); MIM number: 480000 OMIM: http://www.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?480000 | |
| ePath X (inactive)-specific transcript (XIST); MIM number: 314670 OMIM: http://www.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?314670 | |
