View source for Biology:X chromosome

{{Short description|Sex chromosome present in both sexes in the XY and X0 sex-determination systems}}
{{Infobox chromosome
| name = Human X chromosome
| image = Human male karyotpe high resolution - X chromosome cropped.png
| caption = Human  X chromosome (after [[Biology:G banding|G-banding]])
| image2 = Human male karyotpe high resolution - Chromosome X.png
| caption2 =  X chromosome in human male karyogram
| length_bp = 154,259,566 bp<br />(CHM13)
| genes = 804 ([[Biology:Consensus CDS Project|CCDS]])<ref name="CCDS"/>
| type = Allosome
| centromere_position = [[Biology:Centromere#Submetacentric|Submetacentric]]<ref name="StrachanRead2010">{{cite book|author1=Tom Strachan|author2=Andrew Read|title=Human Molecular Genetics|url=https://books.google.com/books?id=dSwWBAAAQBAJ&pg=PA45|date=2 April 2010|publisher=Garland Science|isbn=978-1-136-84407-2|page=45}}</ref><br />(61.0 Mbp)<ref name="850bphs">Genome Decoration Page, NCBI. [http://ftp.ncbi.nlm.nih.gov/pub/gdp/ideogram_9606_GCF_000001305.14_850_V1 Ideogram data for Homo sapience (850 bphs, Assembly GRCh38.p3)]. Last update 2014-06-03. Retrieved 2017-04-26.</ref>
| chr = X
| ensembl_id = X
| entrez_id = X
| ncbi_id = X
| ucsc_id = X
| refseq_id = NC_000023
| genbank_id = CM000685
}}

The '''X chromosome''' is one of the two [[Biology:Sex chromosome|sex chromosome]]s in many organisms, including mammals, and is found in both males and females. It is a part of the [[Biology:XY sex-determination system|XY sex-determination system]] and [[Biology:XO sex-determination system|XO sex-determination system]]. The X chromosome was named for its unique properties by early researchers, which resulted in the naming of its counterpart [[Biology:Y chromosome|Y chromosome]], for the next letter in the alphabet, following its subsequent discovery.<ref name="nyt-angier">{{cite web
| url = https://www.nytimes.com/2007/05/01/science/01angi.html
| title = For Motherly X Chromosome, Gender Is Only the Beginning
| last = Angier
| first = Natalie
| work = {{wipe|The New York Times}}
| date = 2007-05-01
| access-date = 2007-05-01}}</ref>

==Discovery==

It was first noted that the X chromosome was special in 1890 by Hermann Henking in Leipzig. Henking was studying the testicles of [[Biology:Pyrrhocoris apterus|'' Pyrrhocoris'']] and noticed that one chromosome did not take part in [[Biology:Meiosis|meiosis]]. Chromosomes are so named because of their ability to take up [[Staining|staining]] (''chroma'' in Greek means ''color''). Although the X chromosome could be stained just as well as the others, Henking was unsure whether it was a different class of the object and consequently named it ''X element'',<ref name=Schwartz/> which later became X chromosome after it was established that it was indeed a chromosome.<ref>David Bainbridge, 'The X in Sex: How the X Chromosome Controls Our Lives'', pages 3-5, Harvard University Press, 2003 {{ISBN|0674016211}}.</ref>

The idea that the X chromosome was named after its similarity to the letter "X" is mistaken. All chromosomes normally appear as an amorphous blob under the microscope and take on a well-defined shape only during mitosis. This shape is vaguely X-shaped for all chromosomes. It is entirely coincidental that the [[Biology:Y chromosome|Y chromosome]], during [[Biology:Mitosis|mitosis]], has two very short branches which can look merged under the microscope and appear as the descender of a Y-shape.<ref>Bainbridge, pages 65-66</ref>

It was first suggested that the X chromosome was involved in sex determination by Clarence Erwin McClung in 1901. After comparing his work on locusts with Henking's and others, McClung noted that only half the sperm received an X chromosome. He called this chromosome an ''accessory chromosome'', and insisted (correctly) that it was a ''proper'' chromosome, and theorized (incorrectly)  that it was the male-determining chromosome.<ref name=Schwartz>James Schwartz, ''In Pursuit of the Gene: From Darwin to DNA'', pages 155-158, Harvard University Press, 2009 {{ISBN|0674034910}}</ref>

==Inheritance pattern==
{{One source section
| date = August 2021
}}[[File:X chromosome ancestral line Fibonacci sequence.svg|thumb|360px|The number of possible ancestors on the X chromosome inheritance line at a given ancestral generation follows the Fibonacci sequence. (After Hutchison, L. "Growing the Family Tree: The Power of DNA in Reconstructing Family Relationships".<ref name="xcs"/>)]]
Luke Hutchison noticed that a number of possible ancestors on the X chromosome inheritance line at a given ancestral generation follows the [[Fibonacci sequence]].<ref name="xcs">{{Cite journal|last=Hutchison|first=Luke|date=September 2004|title=Growing the Family Tree: The Power of DNA in Reconstructing Family Relationships|url=http://fhtw.byu.edu/static/conf/2005/hutchison-growing-fhtw2005.pdf|journal=Proceedings of the First Symposium on Bioinformatics and Biotechnology (BIOT-04)|access-date=2016-09-03}}</ref> A male individual has an X chromosome, which he received from his mother, and a [[Biology:Y chromosome|Y chromosome]], which he received from his father. The male counts as the "origin" of his own X chromosome (<math>F_1=1</math>), and at his parents' generation, his X chromosome came from a single parent (<math>F_2=1</math>). The male's mother received one X chromosome from her mother (the son's maternal grandmother), and one from her father (the son's maternal grandfather), so two grandparents contributed to the male descendant's X chromosome (<math>F_3=2</math>). The maternal grandfather received his X chromosome from his mother, and the maternal grandmother received X chromosomes from both of her parents, so three great-grandparents contributed to the male descendant's X chromosome (<math>F_4=3</math>). Five great-great-grandparents contributed to the male descendant's X chromosome (<math>F_5=5</math>), etc. (Note that this assumes that all ancestors of a given descendant are independent, but if any genealogy is traced far enough back in time, ancestors begin to appear on multiple lines of the genealogy, until eventually, a [[Biology:Founder effect|population founder]] appears on all lines of the genealogy.)

==Humans==
===Function===
[[Image:Sd4hi-unten-crop.jpg|thumb|Nucleus of a female amniotic fluid cell. Top: Both X-chromosome territories are detected by [[Biology:Fluorescence in situ hybridization|FISH]]. Shown is a single optical section made with a confocal microscope. Bottom: Same nucleus stained with DAPI and recorded with a [[Engineering:Charge-coupled device|CCD camera]]. The Barr body is indicated by the arrow, it identifies the inactive X (Xi).
]]
The X chromosome in humans spans more than 153 million base pairs (the building material of [[Biology:DNA|DNA]]). It represents about 800 protein-coding genes compared to the Y chromosome containing about 70 genes, out of 20,000–25,000 total genes in the human genome.
Each person usually has one pair of sex chromosomes in each cell. Females typically have two X chromosomes, whereas males typically have one X and one [[Biology:Y chromosome|Y chromosome]]. Both males and females retain one of their mother's X chromosomes, and females retain their second X chromosome from their father. Since the father retains his X chromosome from his mother, a human female has one X chromosome from her paternal grandmother (father's side), and one X chromosome from her mother. This inheritance pattern follows the Fibonacci numbers at a given ancestral depth.{{cn|date=November 2023}}

[[Medicine:Genetic disorder|Genetic disorder]]s that are due to [[Biology:Mutation|mutation]]s in genes on the X chromosome are described as [[Biology:X-linked recessive inheritance|X linked]]. If the X chromosome has a genetic disease gene, it always causes illness in male patients, since men have only one X chromosome and therefore only one copy of each gene. Females, instead, may stay healthy and only be carrier of genetic illness, since they have another X chromosome and possibility to have healthy gene copy. For example, hemophilia A and B and [[Medicine:Congenital red–green color blindness|congenital red–green color blindness]] run in families this way.

The X chromosome carries hundreds of genes but few, if any, of these have anything to do directly with sex determination. Early in [[Biology:Embryo|embryo]]nic development in females, one of the two X chromosomes is permanently inactivated in nearly all somatic cells (cells other than egg and [[Biology:Spermatozoon|sperm]] cells). This phenomenon is called [[Biology:X-inactivation|X-inactivation]] or Lyonization, and creates a [[Biology:Barr body|Barr body]]. If X-inactivation in the somatic cell meant a complete de-functionalizing of one of the X-chromosomes, it would ensure that females, like males, had only one functional copy of the X chromosome in each somatic cell. This was previously assumed to be the case. However, recent research suggests that the [[Biology:Barr body|Barr body]] may be more biologically active than was previously supposed.<ref name="Carrel">{{cite journal |vauthors=Carrel L, Willard H |title=X-inactivation profile reveals extensive variability in X-linked gene expression in females |journal=Nature |volume=434 |issue=7031 |pages=400–4 |date=2005 |doi=10.1038/nature03479 |pmid=15772666|bibcode=2005Natur.434..400C |s2cid=4358447 }}</ref>

The partial [[Biology:X-inactivation|inactivation of the X-chromosome]] is due to repressive [[Biology:Heterochromatin|heterochromatin]] that compacts the DNA and prevents the expression of most genes.  Heterochromatin compaction is regulated by Polycomb Repressive Complex 2 ([[Biology:PRC2|PRC2]]).<ref name="pmid28758948">{{cite journal |vauthors=Veneti Z, Gkouskou KK, Eliopoulos AG |title=Polycomb Repressor Complex 2 in Genomic Instability and Cancer |journal=Int J Mol Sci |volume=18 |issue=8 |pages= 1657|date=July 2017 |pmid=28758948 |pmc=5578047 |doi=10.3390/ijms18081657 |doi-access=free }}</ref>

===Genes===
==== Number of genes ====
The following are some of the gene count estimates of human X chromosome. Because researchers use different approaches to genome annotation their predictions of the number of genes on each chromosome varies (for technical details, see [[Gene prediction|gene prediction]]). Among various projects, the collaborative consensus coding sequence project ([[Biology:Consensus CDS 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.<ref name="pmid20441615">{{cite journal| author=Pertea M, Salzberg SL| title=Between a chicken and a grape: estimating the number of human genes | journal=Genome Biol | date= 2010 | volume= 11 | issue= 5 | pages= 206 | pmid=20441615 | doi=10.1186/gb-2010-11-5-206 | pmc=2898077 | doi-access=free }}</ref>

{| class="wikitable" style="text-align:right"
|-
! Estimated by
! Protein-coding genes
! [[Biology:Non-coding RNA|Non-coding RNA gene]]s
! [[Biology:Pseudogene|Pseudogene]]s
! Source
! Release date
|-
| [[Biology:Consensus CDS Project|CCDS]] || 804 || — || —
|style="text-align:center"| <ref name="CCDS">{{cite web | title=Search results - X&#91;CHR&#93; AND "Homo sapiens"&#91;Organism&#93; AND ("has ccds"&#91;Properties&#93; AND alive&#91;prop&#93;) - Gene | website= NCBI |version = CCDS Release 20 for ''Homo sapiens'' | url=https://www.ncbi.nlm.nih.gov/gene?term=X%5BChr%5D%20AND%20%22Homo%20sapiens%22%5BOrganism%5D%20AND%20%28%22has%20ccds%22%5BProperties%5D%20AND%20alive%5Bprop%5D%29&cmd=DetailsSearch |date=2016-09-08 | access-date=2017-05-28}}</ref>
| 2016-09-08
|-
| [[Organization:HUGO Gene Nomenclature Committee|HGNC]]|| 825 || 260 || 606
|style="text-align:center"| <ref name="HGNC20170512">{{cite web | title=Statistics & Downloads for chromosome X | website=HUGO Gene Nomenclature Committee | url=https://www.genenames.org/cgi-bin/statistics?c=X  |date=2017-05-12 | access-date=2017-05-19}}</ref>
| 2017-05-12
|-
| [[Biology:Ensembl genome database project|Ensembl]] || 841 || 639 || 871
|style="text-align:center"| <ref name="Ensembl Release 88">{{cite web | title=Chromosome X: Chromosome summary - Homo sapiens | website= Ensembl Release 88 | url=http://mar2017.archive.ensembl.org/Homo_sapiens/Location/Chromosome?r=X |date=2017-03-29 | access-date=2017-05-19}}</ref>
| 2017-03-29
|-
| [[Biology:UniProt|UniProt]] || 839 || — || —
|style="text-align:center"| <ref name="UniProt">{{cite web | title=Human chromosome X: entries, gene names and cross-references to MIM | website= UniProt | url=https://www.uniprot.org/docs/humchrx.txt |date=2018-02-28 | access-date=2018-03-16}}</ref>
| 2018-02-28
|-
| [[Organization:National Center for Biotechnology Information|NCBI]] || 874 || 494 || 879
|style="text-align:center"| <ref name="NCBI coding">{{cite web | title=Search results - X&#91;CHR&#93; AND "Homo sapiens"&#91;Organism&#93; AND ("genetype protein coding"&#91;Properties&#93; AND alive&#91;prop&#93;) - Gene | website=NCBI | date=2017-05-19 | url=https://www.ncbi.nlm.nih.gov/gene?term=X%5BCHR%5D%20AND%20%22Homo%20sapiens%22%5BOrganism%5D%20AND%20%28%22genetype%20protein%20coding%22%5BProperties%5D%20AND%20alive%5Bprop%5D%29&cmd=DetailsSearch | access-date=2017-05-20}}</ref><ref name="NCBI noncoding">{{cite web | title=Search results - X&#91;CHR&#93; AND "Homo sapiens"&#91;Organism&#93; AND ( ("genetype miscrna"&#91;Properties&#93; OR "genetype ncrna"&#91;Properties&#93; OR "genetype rrna"&#91;Properties&#93; OR "genetype trna"&#91;Properties&#93; OR "genetype scrna"&#91;Properties&#93; OR "genetype snrna"&#91;Properties&#93; OR "genetype snorna"&#91;Properties&#93;) NOT "genetype protein coding"&#91;Properties&#93; AND alive&#91;prop&#93;) - Gene | website=NCBI | date=2017-05-19 | url=https://www.ncbi.nlm.nih.gov/gene?term=X%5BCHR%5D%20AND%20%22Homo%20sapiens%22%5BOrganism%5D%20AND%20%28%28%22genetype%20miscrna%22%5BProperties%5D%20OR%20%22genetype%20ncrna%22%5BProperties%5D%20OR%20%22genetype%20rrna%22%5BProperties%5D%20OR%20%22genetype%20trna%22%5BProperties%5D%20OR%20%22genetype%20scrna%22%5BProperties%5D%20OR%20%22genetype%20snrna%22%5BProperties%5D%20OR%20%22genetype%20snorna%22%5BProperties%5D%29%20NOT%20%22genetype%20protein%20coding%22%5BProperties%5D%20AND%20alive%5Bprop%5D%29&cmd=DetailsSearch | access-date=2017-05-20}}</ref><ref name="NCBI pseudo">{{cite web | title=Search results - X&#91;CHR&#93; AND "Homo sapiens"&#91;Organism&#93; AND ("genetype pseudo"&#91;Properties&#93; AND alive&#91;prop&#93;) - Gene | website=NCBI | date=2017-05-19 | url=https://www.ncbi.nlm.nih.gov/gene?term=X%5BCHR%5D%20AND%20%22Homo%20sapiens%22%5BOrganism%5D%20AND%20%28%22genetype%20pseudo%22%5BProperties%5D%20AND%20alive%5Bprop%5D%29&cmd=DetailsSearch | access-date=2017-05-20}}</ref>
| 2017-05-19
|}

==== Gene list ====
{{Category see also|Genes on human chromosome X}}
The following is a partial list of genes on human chromosome X. For complete list, see the link in the infobox on the right.
{{columns-list|
* [[Biology:AD16 (gene)|AD16]]: encoding Alzheimer disease 16 protein
* [[Biology:AIC (gene)|AIC]]: encoding protein AIC
* [[Biology:Apolipoprotein O|APOO]]: encoding protein Apolipoprotein O
* [[Biology:ARMCX6|ARMCX6]]: encoding protein Armadillo repeat containing X-linked 6
* [[Biology:Protein BEX1|BEX1]]: encoding protein Brain-expressed X-linked protein 1
* BEX2: encoding protein Brain-expressed X-linked protein 2
* [[Biology:BEX4|BEX4]]: encoding protein Brain expressed, X-linked 4
* [[Biology:Coiled-coil domain containing protein 120|CCDC120]]: encoding protein Coiled coil domain containing protein 120
* [[Biology:CCDC22|CCDC22]]: encoding protein Coiled-coil domain containing 22
* [[Biology:CD99L2|CD99L2]]: CD99 antigen-like protein 2
* CDR1-AS: encoding protein CDR1 antisense RNA
* [[Biology:CFAP47|CFAP47]]: encoding protein Cilia and flagella associated protein 47
* CHRDL1: encoding protein Chordin-like 1
* [[Biology:CMTX2|CMTX2]] encoding protein Charcot-Marie-Tooth neuropathy, X-linked 2 (recessive)
* [[Biology:CMTX3|CMTX3]] encoding protein Charcot-Marie-Tooth neuropathy, X-linked 3 (dominant)
* CT45A5: encoding protein Cancer/testis antigen family 45, member A5
* CT55: encoding protein Cancer/testis antigen 55
* [[Biology:CXorf36|CXorf36]]: encoding protein hypothetical protein LOC79742
* CXorf57: encoding protein Chromosome X [[Biology:Open reading frame|open reading frame]] 57
* [[Biology:CXorf40A|CXorf40A]]: Chromosome X open reading frame 40
* [[Biology:CXorf49|CXorf49]]: chromosome X open reading frame 49. encoding protein
* [[Biology:CXorf66|CXorf66]]: encoding protein Chromosome X Open Reading Frame 66
* [[Biology:CXorf67|CXorf67]]: encoding protein Uncharacterized protein CXorf67
* [[Biology:DACH2|DACH2]]: encoding protein Dachshund homolog 2
* EFHC2: encoding protein EF-hand domain (C-terminal) containing 2
* ERCC6L encoding protein ERCC excision repair 6 like, spindle assembly checkpoint helicase
* [[Biology:F8A1|F8A1]]: Factor VIII intron 22 protein
* FAM104B: encoding protein Family with sequence similarity 104 member B
* FAM120C: encoding protein Family with sequence similarity 120C
* FAM122B: Family with sequence similarity 122 member B
* FAM122C: encoding protein Family with sequence similarity 122C
* [[Biology:FAM127A|FAM127A]]: CAAX box protein 1
* [[Biology:FAM50A|FAM50A]]: Family with sequence similarity 50 member A
* [[Biology:FATE1|FATE1]]: Fetal and adult testis-expressed transcript protein
* [[Biology:FMR1-AS1 gene|FMR1-AS1]]: encoding a [[Biology:Long non-coding RNA|long non-coding RNA]] FMR1 antisense RNA 1
* [[Biology:FRMPD3|FRMPD3]]: encoding protein FERM and PDZ domain containing 3
* [[Biology:FRMPD4|FRMPD4]]: encoding protein FERM and PDZ domain containing 4
* FUNDC1: encoding protein FUN14 domain containing 1
* FUNDC2: FUN14 domain-containing protein 2
* GAGE12F: encoding G antigen 12F protein
* GAGE2A: encoding G antigen 2A protein
* [[Biology:GATA1|GATA1]]: encoding [[Biology:GATA1|GATA1 transcription factor]]
* GNL3L encoding protein G protein nucleolar 3 like
* [[Biology:GPRASP2|GPRASP2]]: G-protein coupled receptor-associated sorting protein 2
* [[Biology:GRIPAP1|GRIPAP1]]: encoding protein GRIP1-associated protein 1
* [[Biology:GRDX|GRDX]]: encoding protein Graves disease, susceptibility to, X-linked
* [[Biology:HDHD1A|HDHD1A]]: encoding [[Biology:Enzyme|enzyme]] Haloacid dehalogenase-like hydrolase domain-containing protein 1A
* HS6ST2: encoding protein Heparan sulfate 6-O-sulfotransferase 2
* [[Organization:ITM2A|ITM2A]]: encoding protein Integral membrane protein 2A
* [[Biology:LAS1L|LAS1L]]: encoding protein LAS1-like protein
* [[Biology:LINC01420|LINC01420]]: encoding protein Nucleosome assembly protein 1 like 3
* [[Biology:LOC101059915|LOC101059915]]: encoding *LOC101059915 protein
* [[Biology:MAGEA2|MAGEA2]]: encoding protein Melanoma-associated antigen 2
* [[Biology:MAGEA5|MAGEA5]]: encoding protein Melanoma antigen family A, 5
* [[Biology:Melanoma antigen family a, 8|MAGEA8]]: encoding protein Melanoma antigen family A, 8
* [[Biology:MAGED4B|MAGED4B]]: encoding protein Melanoma-associated antigen D4
* MAGT1: encoding protein Magnesium transporter protein 1
* MAGED4: encoding protein MAGE family member D4
* [[Biology:MAP3K15|MAP3K15]]: encoding protein Mitogen-activated protein kinase kinase kinase 15
* [[Biology:MBNL3|MBNL3]]: encoding protein Muscleblind-like protein 3
* MBTPS2: encoding [[Biology:Enzyme|enzyme]] Membrane-bound transcription factor site-2 protease
* MCT-1: encoding protein MCTS1, re-initiation and release factor
* MIR106A: encoding [[Biology:MicroRNA|microRNA]] MicroRNA 106
* MIR222: encoding [[Biology:MicroRNA|microRNA]] MicroRNA 222
* MIR223: encoding protein MicroRNA 223
* [[Biology:MIR361|MIR361]]: encoding [[Biology:MicroRNA|microRNA]] MicroRNA 361
* MIR503: encoding [[Biology:MicroRNA|microRNA]] MicroRNA 503
* MIR6087: encoding [[Biology:MicroRNA|microRNA]] MicroRNA 6087
* MIR660: encoding [[Biology:MicroRNA|microRNA]] MicroRNA 660
* MIRLET7F2: encoding protein MicroRNA let-7f-2
* [[Biology:MORF4L2|MORF4L2]]: encoding protein Mortality factor 4-like protein 2
* MOSPD1: encoding protein Motile sperm domain containing 1
* MOSPD2: encoding protein Motile sperm domain containing 2
* NAP1L3: encoding protein Nucleosome assembly protein 1 like 3
* [[Biology:NKRF (gene)|NKRF]]: encoding protein NF-kappa-B-repressing factor
* [[Biology:NRK (gene)|NRK]]: encoding [[Biology:Enzyme|enzyme]] Nik-related protein kinase
* OTUD5: encoding protein OTU deubiquitinase 5
* [[Biology:PASD1|PASD1]]: encoding protein PAS domain-containing protein 1
* PAGE1: encoding protein PAGE family member 1
* PAGE2B: encoding PAGE family member 2B protein
* [[Biology:PBDC1|PBDC1]]: encoding a protein of unestablished function
* [[Biology:PCYT1B|PCYT1B]]: encoding [[Biology:Enzyme|enzyme]] Choline-phosphate cytidylyltransferase B
* [[Biology:Peptidyl-prolyl cis-trans isomerase NIMA-interacting 4|PIN4]]: encoding [[Biology:Enzyme|enzyme]] Peptidyl-prolyl cis-trans isomerase NIMA-interacting 4
* [[Biology:PLAC1|PLAC1]]: encoding protein Placenta-specific protein 1
* [[Biology:PLP2|PLP2]]: encoding protein Proteolipid protein 2
* [[Biology:PRR32|PRR32]]: encoding protein PRR32
* [[Biology:RPA4|RPA4]]: encoding protein Replication protein A 30 kDa subunit
* [[Biology:RPS6KA6|RPS6KA6]]: encoding protein Ribosomal protein S6 kinase, 90kDa, polypeptide 6
* [[Biology:RRAGB|RRAGB]]: encoding protein Ras-related GTP-binding protein B
* RTL3: encoding protein Retrotransposon Gag like 3
* [[Biology:SFRS17A|SFRS17A]]: encoding protein Splicing factor, arginine/serine-rich 17A
* SLC38A5: encoding protein Solute carrier family 38 member 5
* SLITRK2: encoding protein SLIT and NTRK-like protein 2
* [[Biology:SMARCA1|SMARCA1]]: encoding protein Probable global transcription activator SNF2L1
* SMS: encoding [[Biology:Enzyme|enzyme]] Spermine synthase
* SPANXN1: encoding protein SPANX family member N1
* SPANXN5: encoding protein SPANX family member N5
* SPG16: encoding protein Spastic paraplegia 16 (complicated, X-linked recessive)
* [[Biology:SSR4|SSR4]]: encoding protein Translocon-associated protein subunit delta
* TAF7L: encoding protein TATA-box binding protein associated factor 7-like
* [[Biology:TCEAL1|TCEAL1]]: encoding protein Transcription elongation factor A protein-like 1
* [[Biology:TCEAL4|TCEAL4]]: encoding protein Transcription elongation factor A protein-like 4
* TENT5D: encoding protein Terminal nucleotidyltransferase 5D
* TEX11: encoding protein Testis expressed 11
* [[Biology:THOC2|THOC2]]: encoding protein THO complex subunit 2
* [[Biology:TMEM29|TMEM29]]: encoding protein Protein FAM156A
* TMEM47: encoding protein Transmembrane protein 47
* TMLHE: encoding [[Biology:Enzyme|enzyme]] Trimethyllysine dioxygenase, mitochondrial
* TNMD encoding protein Tenomodulin (also referred to as tendin, myodulin, Tnmd and TeM)
* [[Biology:SEDLP|TRAPPC2P1]] encoding protein Trafficking protein particle complex subunit 2
* TREX2: encoding [[Biology:Enzyme|enzyme]] Three prime repair exonuclease 2
* TRO: encoding protein Trophinin
* TSPYL2: encoding protein Testis-specific Y-encoded-like protein 2
* [[Biology:TTC3P1|TTC3P1]]: encoding protein Tetratricopeptide repeat domain 3 pseudogene 1
* [[Biology:USP51|USP51]]: encoding [[Biology:Enzyme|enzyme]] Ubiquitin carboxyl-terminal hydrolase 51
* VSIG1: encoding protein V-set and immunoglobulin domain containing 1
* YIPF6: encoding protein Protein YIPF6
* ZC3H12B: encoding protein ZC3H12B
* [[Biology:ZC4H2 deficiency|ZC4H2]]: encoding protein ZC4H2 Deficiency
* ZCCHC18: encoding protein Zinc finger CCHC-type containing 18
* [[Biology:ZFP92|ZFP92]]: encoding protein ZFP92 zinc finger protein
* [[Biology:ZMYM3|ZMYM3]]: encoding protein Zinc finger MYM-type protein 3
* [[Biology:Zinc finger protein 157|ZNF157]]: encoding protein Zinc finger protein 157
* [[Biology:ZNF182|ZNF182]] encoding protein Zinc finger protein 182
* ZNF275: encoding protein Zinc finger protein 275
* [[Biology:Zinc finger protein 674|ZNF674]]: encoding protein Zinc finger protein 674
}}

===Structure===

It is theorized by Ross et al. 2005 and Ohno 1967 that the X chromosome is at least partially derived from the autosomal (non-sex-related) genome of other mammals, evidenced from interspecies genomic sequence alignments.

The X chromosome is notably larger and has a more active [[Biology:Euchromatin|euchromatin]] region than its [[Biology:Y chromosome|Y chromosome]] counterpart. Further comparison of the X and Y reveal regions of homology between the two. However, the corresponding region in the Y appears far shorter and lacks regions that are conserved in the X throughout primate species, implying a genetic degeneration for Y in that region. Because males have only one X chromosome, they are more likely to have an X chromosome-related disease.

It is estimated that about 10% of the genes encoded by the X chromosome are associated with a family of "CT" genes, so named because they encode for markers found in both tumor cells (in cancer patients) as well as in the human testis (in healthy patients).<ref name="ross">{{cite journal  |vauthors=Ross M, etal |title=The DNA sequence of the human X chromosome |journal=Nature |volume=434 |issue=7031 |pages=325–37 |date=2005 |doi=10.1038/nature03440 |pmid=15772651 |pmc=2665286|bibcode=2005Natur.434..325R }}</ref>

===Role in disease===
====Numerical abnormalities====
[[Medicine:Klinefelter syndrome|Klinefelter syndrome]]:
* Klinefelter syndrome is caused by the presence of one or more extra copies of the X chromosome in a male's cells.
* Males with Klinefelter syndrome typically have one extra copy of the X chromosome in each cell, for a total of two X chromosomes and one Y chromosome (47,XXY). It is less common for affected males to have two or three extra X chromosomes (48,XXXY or 49,XXXXY) or extra copies of both the X and Y chromosomes (48,XXYY) in each cell. The extra genetic material may lead to tall stature, learning and reading disabilities, and other medical problems. Each extra X chromosome lowers the child's IQ by about 15 points,<ref>{{cite web|url=http://emedicine.medscape.com/article/945649-overview#a0104|author1=Harold Chen |author2=Ian Krantz |author3=Mary L Windle |author4=Margaret M McGovern |author5=Paul D Petry |author6=Bruce Buehler |date=2013-02-22 | access-date=2014-07-18 | title=Klinefelter Syndrome Pathophysiology |website=Medscape}}</ref><ref>{{cite journal |vauthors=Visootsak J, Graham JM |title=Klinefelter syndrome and other sex chromosomal aneuploidies |journal=Orphanet J Rare Dis |volume=1 |pages=42 |date=2006 |pmid=17062147 |pmc=1634840 |doi=10.1186/1750-1172-1-42 |doi-access=free }}</ref> which means that the average IQ in Klinefelter syndrome is in general in the normal range, although below average. When additional X and/or Y chromosomes are present in 48,XXXY, 48,XXYY, or 49,XXXXY, developmental delays and cognitive difficulties can be more severe and mild [[Medicine:Intellectual disability|intellectual disability]] may be present.
* Klinefelter syndrome can also result from an extra X chromosome in only some of the body's cells. These cases are called mosaic 46,XY/47,XXY.

[[Medicine:Trisomy X|Trisomy X]]
* This syndrome results from an extra copy of the X chromosome in each of a female's cells. Females with trisomy X have three X chromosomes, for a total of 47 chromosomes per cell. The average IQ of females with this syndrome is 90, while the average IQ of unaffected siblings is 100.<ref>{{cite book|vauthors=Bender B, Puck M, Salbenblatt J, Robinson A |title=Cognitive development of children with sex chromosome abnormalities |editor=Smith S |location=San Diego |publisher=College Hill Press |date=1986|pages=175–201}}</ref> Their stature on average is taller than normal females. They are fertile and their children do not inherit the condition.<ref>{{cite web|url=http://ghr.nlm.nih.gov/condition/triple-x-syndrome | title=Triple X syndrome | website=Genetics Home Reference | date=2014-07-14 | access-date=2014-07-18}}</ref>
* Females with more than one extra copy of the X chromosome (48, [[Medicine:Tetrasomy X|tetrasomy X]] or 49, [[Medicine:Pentasomy X|pentasomy X]]) have been identified, but these conditions are rare.

[[Medicine:Turner syndrome|Turner syndrome]]:
* This results when each of a female's cells has one normal X chromosome and the other sex chromosome is missing or altered. The missing genetic material affects development and causes the features of the condition, including short stature and infertility.
* About half of individuals with Turner syndrome have [[Medicine:Monosomy|monosomy]] X (45,X), which means each cell in a woman's body has only one copy of the X chromosome instead of the usual two copies. Turner syndrome can also occur if one of the sex chromosomes is partially missing or rearranged rather than completely missing. Some women with Turner syndrome have a chromosomal change in only some of their cells. These cases are called Turner syndrome mosaics (45,X/46,XX).

==== X-linked recessive disorders ====
[[Biology:Sex linkage|Sex linkage]] was first discovered in insects, e.g., [[Biography:Thomas Hunt Morgan|T. H. Morgan]]'s 1910 discovery of the pattern of inheritance of  the white eyes mutation in ''[[Biology:Drosophila melanogaster|Drosophila melanogaster]]''.<ref>{{Cite journal|last=Morgan|first=T. H.|date=1910|title=Sex-limited inheritance in Drosophila|url=https://zenodo.org/record/1448044|journal=Science|volume=32|issue=812|pages=120–122|doi=10.1126/science.32.812.120|pmid=17759620|bibcode=1910Sci....32..120M}}</ref>  Such discoveries helped to explain x-linked disorders in humans, e.g., [[Medicine:Haemophilia|haemophilia]] A and B, [[Medicine:Adrenoleukodystrophy|adrenoleukodystrophy]], and [[Medicine:Color blindness|red-green color blindness]].

====Other disorders====
[[Medicine:XX male syndrome|XX male syndrome]] is a rare disorder, where the SRY region of the Y chromosome has recombined to be located on one of the X chromosomes. As a result, the XX combination after fertilization has the same effect as a XY combination, resulting in a male. However, the other genes of the X chromosome cause feminization as well.

[[Medicine:X-linked endothelial corneal dystrophy|X-linked endothelial corneal dystrophy]] is an extremely rare disease of cornea associated with Xq25 region. Lisch epithelial corneal dystrophy is associated with Xp22.3.

Megalocornea 1 is associated with Xq21.3-q22{{Medical citation needed|date=November 2015}}

[[Medicine:Adrenoleukodystrophy|Adrenoleukodystrophy]], a rare and fatal disorder that is carried by the mother on the x-cell. It affects only boys between the ages of 5 and 10 and destroys the protective cell surrounding the nerves, [[Biology:Myelin|myelin]], in the brain. The female carrier hardly shows any symptoms because females have a copy of the x-cell. This disorder causes a once healthy boy to lose all abilities to walk, talk, see, hear, and even swallow. Within 2 years after diagnosis, most boys with Adrenoleukodystrophy die.

===Cytogenetic band===
[[File:Human chromosome X ideogram vertical.svg|thumb|G-banding ideogram of human X chromosome 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).|border|833x833px]]
[[File:Human chromosome X - 400 550 850 bphs.png|thumb|G-banding patterns of human X chromosome in three different resolutions (400,<ref name="400bphs">Genome Decoration Page, NCBI. [http://ftp.ncbi.nlm.nih.gov/pub/gdp/ideogram_9606_GCF_000001305.14_400_V1 Ideogram data for Homo sapience (400 bphs, Assembly GRCh38.p3)]. Last update 2014-03-04. Retrieved 2017-04-26.</ref> 550<ref name="550bphs">Genome Decoration Page, NCBI.   [http://ftp.ncbi.nlm.nih.gov/pub/gdp/ideogram_9606_GCF_000001305.14_550_V1 Ideogram data for Homo sapience (550 bphs, Assembly GRCh38.p3)]. Last update 2015-08-11. Retrieved 2017-04-26.</ref> and 850<ref name="850bphs" /> Band length in this diagram is based on the ideograms from ISCN (2013).<ref name="Nomenclature2013">{{cite book|author=International Standing Committee on Human Cytogenetic Nomenclature|url=https://books.google.com/books?id=lGCLrh0DIwEC|title=ISCN 2013: An International System for Human Cytogenetic Nomenclature (2013)|publisher=Karger Medical and Scientific Publishers|date=2013|isbn=978-3-318-02253-7}}</ref> This type of ideogram represents actual relative band length observed under a microscope at the different moments during the [[Biology:Mitosis|mitotic process]].<ref name="SethakulvichaiManitpornsut2012">{{Cite book|last1=Sethakulvichai|first1=W.|url=https://www.researchgate.net/publication/261304470|last2=Manitpornsut|first2=S.|last3=Wiboonrat|first3=M.|last4=Lilakiatsakun|first4=W.|last5=Assawamakin|first5=A.|last6=Tongsima|first6=S.|title=2012 Ninth International Conference on Computer Science and Software Engineering (JCSSE) |chapter=Estimation of band level resolutions of human chromosome images |date=2012|isbn=978-1-4673-1921-8|pages=276–282|doi=10.1109/JCSSE.2012.6261965|s2cid=16666470}}</ref>|450x450px]]
{| class="wikitable" style="text-align:right"
|+ [[Biology:G banding|G-band]]s of human X chromosome in resolution 850 bphs<ref name="850bphs"/>
! Chr.
! Arm<ref>"'''p'''": Short arm; "'''q'''": Long arm.</ref>
! Band<ref>For cytogenetic banding nomenclature, see article [[Biology:Locus (genetics)|locus]].</ref>
! ISCN<br />start<ref name="ISCN">These 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]].</ref>
! ISCN<br />stop<ref name="ISCN"/>
! Basepair<br />start
! Basepair<br />stop
! Stain<ref>'''gpos''': Region which is positively stained by [[Biology:G banding|G banding]], generally [[Biology:GC-content|AT-rich]] and gene poor; '''gneg''': Region which is negatively stained by G banding, generally [[Biology:GC-content|CG-rich]] and gene rich; '''acen''' [[Biology:Centromere|Centromere]]. '''var''': Variable region; '''stalk''': Stalk.</ref>
! Density
|-
| X || p
|style="text-align:left"| 22.33 || 0 || 323 || {{val|1|fmt=commas}} || {{val|4400000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || p
|style="text-align:left"| 22.32 || 323 || 504 || {{val|4400001|fmt=commas}} || {{val|6100000|fmt=commas}}
|style="background:#979797"| gpos || 50
|-
| X || p
|style="text-align:left"| 22.31 || 504 || 866 || {{val|6100001|fmt=commas}} || {{val|9600000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || p
|style="text-align:left"| 22.2 || 866 || 1034 || {{val|9600001|fmt=commas}} || {{val|17400000|fmt=commas}}
|style="background:#979797"| gpos || 50
|-
| X || p
|style="text-align:left"| 22.13 || 1034 || 1345 || {{val|17400001|fmt=commas}} || {{val|19200000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || p
|style="text-align:left"| 22.12 || 1345 || 1448 || {{val|19200001|fmt=commas}} || {{val|21900000|fmt=commas}}
|style="background:#979797"| gpos || 50
|-
| X || p
|style="text-align:left"| 22.11 || 1448 || 1577 || {{val|21900001|fmt=commas}} || {{val|24900000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || p
|style="text-align:left"| 21.3 || 1577 || 1784 || {{val|24900001|fmt=commas}} || {{val|29300000|fmt=commas}}
|style="background:black; color:white;"| gpos || 100
|-
| X || p
|style="text-align:left"| 21.2 || 1784 || 1862 || {{val|29300001|fmt=commas}} || {{val|31500000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || p
|style="text-align:left"| 21.1 || 1862 || 2120 || {{val|31500001|fmt=commas}} || {{val|37800000|fmt=commas}}
|style="background:black; color:white;"| gpos || 100
|-
| X || p
|style="text-align:left"| 11.4 || 2120 || 2430 || {{val|37800001|fmt=commas}} || {{val|42500000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || p
|style="text-align:left"| 11.3 || 2430 || 2624 || {{val|42500001|fmt=commas}} || {{val|47600000|fmt=commas}}
|style="background:#636363; color:white;"| gpos || 75
|-
| X || p
|style="text-align:left"| 11.23 || 2624 || 2948 || {{val|47600001|fmt=commas}} || {{val|50100000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || p
|style="text-align:left"| 11.22 || 2948 || 3129 || {{val|50100001|fmt=commas}} || {{val|54800000|fmt=commas}}
|style="background:#d9d9d9"| gpos || 25
|-
| X || p
|style="text-align:left"| 11.21 || 3129 || 3206 || {{val|54800001|fmt=commas}} || {{val|58100000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || p
|style="text-align:left"| 11.1 || 3206 || 3297 || {{val|58100001|fmt=commas}} || {{val|61000000|fmt=commas}}
|style="background:#6e7f8f; color:white;"| acen ||
|-
| X || q
|style="text-align:left"| 11.1 || 3297 || 3491 || {{val|61000001|fmt=commas}} || {{val|63800000|fmt=commas}}
|style="background:#6e7f8f; color:white;"| acen ||
|-
| X || q
|style="text-align:left"| 11.2 || 3491 || 3620 || {{val|63800001|fmt=commas}} || {{val|65400000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || q
|style="text-align:left"| 12 || 3620 || 3827 || {{val|65400001|fmt=commas}} || {{val|68500000|fmt=commas}}
|style="background:#979797"| gpos || 50
|-
| X || q
|style="text-align:left"| 13.1 || 3827 || 4137 || {{val|68500001|fmt=commas}} || {{val|73000000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || q
|style="text-align:left"| 13.2 || 4137 || 4292 || {{val|73000001|fmt=commas}} || {{val|74700000|fmt=commas}}
|style="background:#979797"| gpos || 50
|-
| X || q
|style="text-align:left"| 13.3 || 4292 || 4447 || {{val|74700001|fmt=commas}} || {{val|76800000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || q
|style="text-align:left"| 21.1 || 4447 || 4732 || {{val|76800001|fmt=commas}} || {{val|85400000|fmt=commas}}
|style="background:black; color:white;"| gpos || 100
|-
| X || q
|style="text-align:left"| 21.2 || 4732 || 4809 || {{val|85400001|fmt=commas}} || {{val|87000000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || q
|style="text-align:left"| 21.31 || 4809 || 5107 || {{val|87000001|fmt=commas}} || {{val|92700000|fmt=commas}}
|style="background:black; color:white;"| gpos || 100
|-
| X || q
|style="text-align:left"| 21.32 || 5107 || 5184 || {{val|92700001|fmt=commas}} || {{val|94300000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || q
|style="text-align:left"| 21.33 || 5184 || 5430 || {{val|94300001|fmt=commas}} || {{val|99100000|fmt=commas}}
|style="background:#636363; color:white;"| gpos || 75
|-
| X || q
|style="text-align:left"| 22.1 || 5430 || 5701 || {{val|99100001|fmt=commas}} || {{val|103300000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || q
|style="text-align:left"| 22.2 || 5701 || 5843 || {{val|103300001|fmt=commas}} || {{val|104500000|fmt=commas}}
|style="background:#979797"| gpos || 50
|-
| X || q
|style="text-align:left"| 22.3 || 5843 || 6050 || {{val|104500001|fmt=commas}} || {{val|109400000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || q
|style="text-align:left"| 23 || 6050 || 6322 || {{val|109400001|fmt=commas}} || {{val|117400000|fmt=commas}}
|style="background:#636363; color:white;"| gpos || 75
|-
| X || q
|style="text-align:left"| 24 || 6322 || 6619 || {{val|117400001|fmt=commas}} || {{val|121800000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || q
|style="text-align:left"| 25 || 6619 || 7059 || {{val|121800001|fmt=commas}} || {{val|129500000|fmt=commas}}
|style="background:black; color:white;"| gpos || 100
|-
| X || q
|style="text-align:left"| 26.1 || 7059 || 7253 || {{val|129500001|fmt=commas}} || {{val|131300000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || q
|style="text-align:left"| 26.2 || 7253 || 7395 || {{val|131300001|fmt=commas}} || {{val|134500000|fmt=commas}}
|style="background:#d9d9d9"| gpos || 25
|-
| X || q
|style="text-align:left"| 26.3 || 7395 || 7602 || {{val|134500001|fmt=commas}} || {{val|138900000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || q
|style="text-align:left"| 27.1 || 7602 || 7808 || {{val|138900001|fmt=commas}} || {{val|141200000|fmt=commas}}
|style="background:#636363; color:white;"| gpos || 75
|-
| X || q
|style="text-align:left"| 27.2 || 7808 || 7886 || {{val|141200001|fmt=commas}} || {{val|143000000|fmt=commas}}
| style="background:white"| gneg ||
|-
| X || q
|style="text-align:left"| 27.3 || 7886 || 8145 || {{val|143000001|fmt=commas}} || {{val|148000000|fmt=commas}}
|style="background:black; color:white;"| gpos || 100
|-
| X || q
|style="text-align:left"| [[Biology:Xq28|28]] || 8145 || 8610 || {{val|148000001|fmt=commas}} || {{val|156040895|fmt=commas}}
| style="background:white"| gneg ||
|}

[[File:Human chromosome X ideogram.svg|frameless|602x602px]]

===Research===
In July 2020 scientists reported the first complete and gap-less [[Biology:Sequence assembly|assembly]] of a human X chromosome.<ref>{{cite news |title=Scientists achieve first complete assembly of human X chromosome |url=https://phys.org/news/2020-07-scientists-human-chromosome.html |access-date=16 August 2020 |work=phys.org |language=en}}</ref><ref>{{cite journal|last1=Miga|first1=Karen H.|last2=Koren|first2=Sergey|last3=Rhie|first3=Arang|last4=Vollger|first4=Mitchell R.|last5=Gershman|first5=Ariel|last6=Bzikadze|first6=Andrey|last7=Brooks|first7=Shelise|last8=Howe|first8=Edmund|last9=Porubsky|first9=David|last10=Logsdon|first10=Glennis A.|last11=Schneider|first11=Valerie A.|date=14 July 2020|title=Telomere-to-telomere assembly of a complete human X chromosome|journal=Nature|language=en|pages=79–84|doi=10.1038/s41586-020-2547-7|issn=1476-4687|first37=Nadine|last38=Loose|first38=Matthew|last39=Surti|first39=Urvashi|last40=Risques|first40=Rosa ana|first44=Benedict|last41=Lindsay|first41=Tina A. Graves|last42=Fulton|first42=Robert|last43=Hall|first43=Ira|last44=Paten|last52=Eichler|last45=Howe|last50=Gerton|first53=Adam M.|last53=Phillippy|first52=Evan E.|first36=Nicholas J.|first51=Beth A.|last51=Sullivan|first50=Jennifer L.|first49=Pavel A.|first45=Kerstin|last49=Pevzner|first48=James C.|last48=Mullikin|first47=Alice|last47=Young|first46=Winston|last46=Timp|last37=Holmes|last31=Dennis|last36=Loman|last17=Pak|first21=Valerie|last21=Maduro|first20=Christopher|last20=Markovic|first19=Milinn|last19=Kremitzki|first18=Kristof|last18=Tigyi|first17=Evgenia|first16=Jeanne|first22=Amalia|last16=Fredrickson|first15=Joel|last15=Armstrong|first14=William|last14=Chow|first13=Jonathan|last13=Wood|first12=Tamara|last12=Potapova|last22=Dutra|last23=Bouffard|first35=Josh|first29=Jon-Matthew|last35=Quick|first34=Gulhan|last34=Kaya|first33=Ruta|last33=Sahasrabudhe|first32=Daniela C.|last32=Soto|first31=Megan Y.|last30=Selvaraj|last29=Belton|first23=Gerard G.|first28=Anthony D.|last28=Schmitt|first27=Françoise|last27=Thibaud-Nissen|first26=Amy B.|last26=Wilfert|first25=Nancy F.|last25=Hansen|first24=Alexander M.|last24=Chang|first30=Siddarth|volume=585|issue=7823|pmid=32663838|pmc=7484160|bibcode=2020Natur.585...79M|doi-access=free}}</ref>

==See also==
* [[Biology:List of X-STR markers|List of X-STR markers]]
* [[Biology:Sex linkage|Sex linkage]]
* [[Biology:X-inactivation|X-inactivation]]
* [[Biology:Pseudoautosomal region|Pseudoautosomal region]]
* [[Biology:Y chromosome|Y chromosome]]

==References==<!-- CytogenetGenomeRes101:266. -->
* ''Earlier versions of this article contain material from the [https://web.archive.org/web/20081122151614/http://www.nlm.nih.gov/copyright.html National Library of Medicine], a part of the National Institutes of Health (USA,) which, as a US government publication, is in the public domain.''
{{reflist}}

==External links==
* {{cite web | author= National Institutes of Health | title= X chromosome | website= Genetics Home Reference | url= http://ghr.nlm.nih.gov/chromosome=X | access-date= 2017-05-06 | archive-date= 2007-07-08 | archive-url= https://web.archive.org/web/20070708103848/http://ghr.nlm.nih.gov/chromosome=X | url-status= dead }}
* {{Cite web|url=http://web.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/chromoX.shtml|title=X chromosome|website=Human Genome Project Information Archive 1990–2003|access-date=2017-05-06}}

{{Chromosome genetics}}
{{Sex (biology)}}

{{DEFAULTSORT:X Chromosome}}
[[Category:Chromosomes]]
[[Category:Chromosomes (human)|Chromosome X]]
[[Category:Cytogenetics]]
[[Category:Sex-determination systems]]
[[Category:Genes on human chromosome X|*]]

{{Sourceattribution|X chromosome}}