X chromosome

Embryology - 16 Apr 2024        Expand to Translate
Google Translate - select your language from the list shown below (this will open a new external page)
العربية | català | 中文 | 中國傳統的 | français | Deutsche | עִברִית | हिंदी | bahasa Indonesia | italiano | 日本語 | 한국어 | မြန်မာ | Pilipino | Polskie | português | ਪੰਜਾਬੀ ਦੇ | Română | русский | Español | Swahili | Svensk | ไทย | Türkçe | اردو | ייִדיש | Tiếng Việt    These external translations are automated and may not be accurate. (More? About Translations)

Introduction

Some X chromosome disease genes

A snapshot of the human X chromosome.

• 155 million base pairs
• In contrast to the Y chromosome, the X chromosome contains about 5% of the haploid genome and encodes house-keeping and specialized functions.
• Genes such as Wnt-4 and DAX-1 necessary for initiation of female pathway ovary development
• An early discovery (1961) was that in order to have correct levels of X chromosome gene/protein expression (gene dosage), females must "inactivate" a single copy of the X chromosome in each and every cell. The initiator of the X inactivation process was discovered (1991) to be regulated by a region on the inactivating X chromosome encoding an X inactive specific transcript (XIST), that acts as RNA and does not encode a protein.
• The genetic content of the X chromosome has been strongly conserved between species because these genes have become adapted to working as a single dose - Ohno's law
• X inactivation occurs randomly throughout the embryo, generating a mosaic of maternal and paternally derived X chromosome activity in all tissues and organs. This can be seen in the fur colour of tortoiseshell cats.

In birds, the females have a different sex chromosome, the W chromosome. Though this chromosome does not contain genes that lead to the development of a female. (The male bird has a Z chromosome PMID: 9326938) (More? Chicken Development)

Links: Genital - Female Development | X Inactivation | Genetic abnormality locations chromosomes 21-XY

Some Recent Findings

FOXL2 is a female sex-determining gene in the goat "The origin of sex reversal in XX goats homozygous for the polled intersex syndrome (PIS) mutation was unclear because of the complexity of the mutation that affects the transcription of both FOXL2 and several long noncoding RNAs (lncRNAs). Accumulating evidence suggested that FOXL2 could be the sole gene of the PIS locus responsible for XX sex reversal, the lncRNAs being involved in transcriptional regulation of FOXL2. In this study, using zinc-finger nuclease-directed mutagenesis, we generated several fetuses, of which one XX individual bears biallelic mutations of FOXL2. Our analysis demonstrates that FOXL2 loss of function dissociated from loss of lncRNA expression is sufficient to cause an XX female-to-male sex reversal in the goat model and, as in the mouse model, an agenesis of eyelids. Both developmental defects were reproduced in two newborn animals cloned from the XX FOXL2(-/-) fibroblasts. These results therefore identify FOXL2 as a bona fide female sex-determining gene in the goat. They also highlight a stage-dependent role of FOXL2 in the ovary, different between goats and mice, being important for fetal development in the former but for postnatal maintenance in the latter.

More recent papers

This table allows an automated computer search of the external PubMed database using the listed "Search term" text link. This search now requires a manual link as the original PubMed extension has been disabled. The displayed list of references do not reflect any editorial selection of material based on content or relevance. References also appear on this list based upon the date of the actual page viewing. References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability. More? References | Discussion Page | Journal Searches | 2019 References | 2020 References Search term: X chromosome <pubmed limit=5>X chromosome-determining</pubmed>

Human Chromosomes

Human Idiogram: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | X | Y

X Inactivation

The presence in females of 2 X chromosome raises the issue of gene dosage, in the case of mammals this is regulated by inactivating one of the X chromosomes. To balance expression with the autosomal chromosomes the dosage imbalance is then adjusted by doubling expression of X-linked genes in both sexes. In some other species compensation occurs by increasing the expression of X in males. Links: X Inactivation

Macaque Xi at interphase

Diseases

Some X chromosome disease locations

ICD11

• LD50 Number anomalies of chromosome X
• LD51 Structural anomalies of chromosome X, excluding Turner syndrome

Inheritance Pattern Images

Trisomy X

Trisomy X

External Links

External Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name. Links to any external commercial sites are provided for information purposes only and should never be considered an endorsement. UNSW Embryology is provided as an educational resource with no clinical information or commercial affiliation.

• NCBI Genome View - X chromosome
• Ensembl Ensembl - X chromosome
• OMIM OMIM - Xist

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link

---

Cite this page: Hill, M.A. (2024, April 16) Embryology X chromosome. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/X_chromosome

What Links Here?

© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G