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A personal message from Dr Mark Hill (May 2020)  
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I have decided to take early retirement in September 2020. During the many years online I have received wonderful feedback from many readers, researchers and students interested in human embryology. I especially thank my research collaborators and contributors to the site. The good news is Embryology will remain online and I will continue my association with UNSW Australia. I look forward to updating and including the many exciting new discoveries in Embryology!

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


X chromosome

The female sex chromosome, which following sexual reproduction is inherited from each parent in females, and inherited from the mother in males. This inheritence pattern impacts upon the pattern of genetic disease.
(More? Human idiogram - X | X Inactivation | X-Linked dominant (affected father) | X-Linked dominant (affected mother) | X-Linked recessive (affected father) | X-Linked recessive (carrier mother))

xenotropic virus

Term used to describe a virus that can grow in the cells of a species foreign to the normal host species.
(More? Abnormal Development - Viral Infection

xenotropic murine leukemia virus

(XMLV) A xenotropic virus of the gammaretrovirus genus belonging to the retroviridae family (RNA retrovirus) detected in prostate cancers (40% of patients analysed PMID: 16609730) and also recently associated, potentially as an epiphenomenon, with chronic fatigue syndrome (CFS, 67% of patients analysed Science Online). This virus is closely related to the mouse xenotropic murine leukemia viruses (MuLVs). RNA retroviruses can replicate in a host cell and by reverse transcriptase produce DNA that is then incorporated into the host's genome.
(More? Abnormal Development - Viral Infection | Prostate cancer - PMID 16609730 | Chronic fatigue syndrome - Science Online)


Acronym for the inactive X chromosome.


The name for a non-translated RNA (18 Kb) that is associated with the inactivated X chromosome in female cells to correct for the double gene dosage, 2 copies of the X chromosome.
(More? X Inactivation)

X inactivation

Process that occurs in all cells within females, each cell has 2 copies of the X chromosome (one from father and one from mother) one of copy of which is randomly inactivated throughout the entire body in order to maintain gene dosage. Recent studies have shown that this process starts in female human preimplantation-stage embryos, by accumulation of Xist RNA on one of the two X chromosomes starting around the 8-cell stage.
(More? X Inactivation | PMID 19481196)

X linked

Term used to refer to genes, and genetic diseases, located on the X chromosome. Therefore more likely to be expressed in males, where there is only a single maternal X chromosome.
(More? Human idiogram - X | X Inactivation | X-Linked dominant (affected father) | X-Linked dominant (affected mother) | X-Linked recessive (affected father) | X-Linked recessive (carrier mother))


Acronym for xenotropic murine leukemia virus, a virus detected in prostate cancers and recently associated with chronic fatigue syndrome. Other viruses Epstein-Barr virus, human T-lymphotropic virus (HTLV) types I and II have also previously been associated as an epiphenomenon with chronic fatigue syndrome.

Glossary Comments

Use this page to access brief definitions of specific embryology terms. Additional information can be accessed from links listed at the end of each definition. Glossary from the UNSW Embryology program compiled and written by Dr Mark Hill. Reference material used in preparing this glossary list includes: texts listed on page 1 "Reading" of each notes section, Department of Anatomy Publications, WWW resources from NCBI, NIH, OMIM, NHMRC (Australia), AMA (USA), Office of Rare Diseases (USA), PubMed Medline Dictionaries, MSDS, Merck Manual home edn. and WHO ART terminology (2009).

These notes are for Educational Purposes Only Please email Dr Mark Hill if you wish to make a comment about this current project.

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. (2020, June 1) Embryology X. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/X

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© Dr Mark Hill 2020, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G