lyon hypothesis notes

• BiologyDiscussion.com
• Follow Us On:
• Google Plus
• Publish Now

Dosage Compensation/Lyon’s Hypothesis | Genetics

ADVERTISEMENTS:

In this article we will discuss about:- 1. Dosage Compensation and Sex-Chromatin Bodies 2. Details about Dosage Compensation or Lyon’s Hypothesis 3. Objectives behind the Proposition of Lyon’s Hypothesis and 4. Evidences in Support of Lyon’s Hypo­thesis.

Dosage Compensation and Sex-Chromatin B odies:

In man it has been found that Y-chromosomes are genetically inert in comparison to the X-chromosomes and other chromosomes and only a few genes are present in the human Y-chromosome.

From the above discussion on the chro­mosome numbers of male and female human, it appears that females contain a higher dose of functional gene containing chromosome than males (Female chromosome numbers = 44 + XX and Male chromosome number = 44 + XY).

For many years, geneticists have observed that in some case, female homozygous for the genes in the X-chromosomes do not express a trait more markedly than do hemizygous males. So, it must be a mechanism of “dosage compensation”, through which the effective dosage of genes of the two sexes is made equal or nearly so.

This mechanism of compensating the differential doses of functional sex chromo­somes in male and female human is effected by the inactivation of one X-chromosome in the normal female. The genetically inactive X- chromosome or condensed X-chromosome is called hetero-pychnotic X-chromosome or heterochromatin or sex-chromatin body or Barr body (according to the name of the geneticist M. L. Barr who first observed it) or Drum-stick (according to the shape of the inac­tive X-chromosome).

Of the two X-chromo­somes in females, which X-chromosome becomes inactive is a matter of chance, but it should be remembered that once an X- chromosome has become inactivated, all cells arising from that cell will keep the same inac­tive X-chromosome.

In humans, inactive form of X-chromo­some as a Barr-body have been observed by the sixteenth day of gestation. X-chromosome inactivation occurs in human when two or more X-chromosomes are present.

Details about Dosage Compensation or Lyon’s Hypothesis :

The inactive X hypothesis or the Lyon’s hypothesis or the Dosage Compensation is widely known from 1961 which states that only one of the two X chromosomes in the homogametic sex is functional while the other condenses and is inactivated. The X inacti­vated in some cells would be that from the father, in other cells it would be that from the mother.

Hence any tissue in the body of a woman would be a mosaic of cells which would show dominance of all genes having diffusable products but would remain a fine-­grained mosaic for other intracellular differen­ces.

Such a mosaic of cells might be difficult to demonstrate, particularly among rigid tissues, although cells which can be separated and cloned might show antigenic differences. This hypothesis has stimulated many new investiga­tions, some of which are currently being completed.

Objectives behind the Proposition of Lyon’s H ypothesis:

Lyon was impressed by three observations relating to X chromosome:

1. In normal mammalian females, one of the two X’s is genetically inactive in the soma­tic cells (single active X-hypothesis).

2. Inactivation is random i.e., irrespec­tive of paternal and maternal origin (random inactivation).

3. (a) The inactivation occurs during early ontogeny (early ontogenic differentiation) and (b) The particular X which has thus become inactivated, remains inactive in all the succee­ding cell generation (fixed differentiation).

Evidences in Support of Lyon’s Hypo­thesis :

A. For Single Active X Hypothesis:

1. Bengham (1958) and Russell (1961) noticed that an XO mouse is normal and fer­tile female indicating that the activity of the single X is sufficient for the normal develop­ment of this species.

2. McNeil (1956) recorded the case of “calico-cat” or tortoise-shell cat, usually a heterogygote female with black and yellow patches. Here the dominant X linked coat- color gene producing yellow-color becomes inactivated in some cells, whereas in others this mutant gene produces yellow-color, thus causing a mosaic appearance. Exceptional male “calico” is XXY.

3. X-linked ocular albinism in female heterogygotes causes the mosaic pigmentation of retina showing one active and another inactive X.

4. The late replicating nature of sex chro­matin by H 3 -TdR and very little or no RNA synthesized by Barr body in human body indicate the metabolic activity of one X chromosome.

5. The DNA replication pattern in mam­malian females, for example:

Taylor (1960) — in Chinese haunter,

German (1962) — in human being

Mukherjee & Sinha (1966) — in cow etc. shows a late-replicating X (or inactivated) chromosome.

6. In individuals having XXXY or XXX polysomic conditions:

i) There are 2 late Xs.

ii) 2 sex chromatins and

iii) an apparent inactivity of G6PD genes in all but one X chromosome.

From above discussions it is clear that:

• Search Menu
• Browse content in Arts and Humanities
• Browse content in Archaeology
• Anglo-Saxon and Medieval Archaeology
• Archaeological Methodology and Techniques
• Archaeology by Region
• Archaeology of Religion
• Archaeology of Trade and Exchange
• Biblical Archaeology
• Contemporary and Public Archaeology
• Environmental Archaeology
• Historical Archaeology
• History and Theory of Archaeology
• Industrial Archaeology
• Landscape Archaeology
• Mortuary Archaeology
• Prehistoric Archaeology
• Underwater Archaeology
• Urban Archaeology
• Zooarchaeology
• Browse content in Architecture
• Architectural Structure and Design
• History of Architecture
• Residential and Domestic Buildings
• Theory of Architecture
• Browse content in Art
• Art Subjects and Themes
• History of Art
• Industrial and Commercial Art
• Theory of Art
• Biographical Studies
• Byzantine Studies
• Browse content in Classical Studies
• Classical History
• Classical Philosophy
• Classical Mythology
• Classical Literature
• Classical Reception
• Classical Art and Architecture
• Classical Oratory and Rhetoric
• Greek and Roman Epigraphy
• Greek and Roman Law
• Greek and Roman Papyrology
• Greek and Roman Archaeology
• Late Antiquity
• Religion in the Ancient World
• Digital Humanities
• Browse content in History
• Colonialism and Imperialism
• Diplomatic History
• Environmental History
• Genealogy, Heraldry, Names, and Honours
• Genocide and Ethnic Cleansing
• Historical Geography
• History by Period
• History of Emotions
• History of Agriculture
• History of Education
• History of Gender and Sexuality
• Industrial History
• Intellectual History
• International History
• Labour History
• Legal and Constitutional History
• Local and Family History
• Maritime History
• Military History
• National Liberation and Post-Colonialism
• Oral History
• Political History
• Public History
• Regional and National History
• Revolutions and Rebellions
• Slavery and Abolition of Slavery
• Social and Cultural History
• Theory, Methods, and Historiography
• Urban History
• World History
• Browse content in Language Teaching and Learning
• Language Learning (Specific Skills)
• Language Teaching Theory and Methods
• Browse content in Linguistics
• Applied Linguistics
• Cognitive Linguistics
• Computational Linguistics
• Forensic Linguistics
• Grammar, Syntax and Morphology
• Historical and Diachronic Linguistics
• History of English
• Language Acquisition
• Language Evolution
• Language Reference
• Language Variation
• Language Families
• Lexicography
• Linguistic Anthropology
• Linguistic Theories
• Linguistic Typology
• Phonetics and Phonology
• Psycholinguistics
• Sociolinguistics
• Translation and Interpretation
• Writing Systems
• Browse content in Literature
• Bibliography
• Children's Literature Studies
• Literary Studies (Asian)
• Literary Studies (European)
• Literary Studies (Eco-criticism)
• Literary Studies (Romanticism)
• Literary Studies (American)
• Literary Studies (Modernism)
• Literary Studies - World
• Literary Studies (1500 to 1800)
• Literary Studies (19th Century)
• Literary Studies (20th Century onwards)
• Literary Studies (African American Literature)
• Literary Studies (British and Irish)
• Literary Studies (Early and Medieval)
• Literary Studies (Fiction, Novelists, and Prose Writers)
• Literary Studies (Gender Studies)
• Literary Studies (Graphic Novels)
• Literary Studies (History of the Book)
• Literary Studies (Plays and Playwrights)
• Literary Studies (Poetry and Poets)
• Literary Studies (Postcolonial Literature)
• Literary Studies (Queer Studies)
• Literary Studies (Science Fiction)
• Literary Studies (Travel Literature)
• Literary Studies (War Literature)
• Literary Studies (Women's Writing)
• Literary Theory and Cultural Studies
• Mythology and Folklore
• Shakespeare Studies and Criticism
• Browse content in Media Studies
• Browse content in Music
• Applied Music
• Dance and Music
• Ethics in Music
• Ethnomusicology
• Gender and Sexuality in Music
• Medicine and Music
• Music Cultures
• Music and Religion
• Music and Media
• Music and Culture
• Music Education and Pedagogy
• Music Theory and Analysis
• Musical Scores, Lyrics, and Libretti
• Musical Structures, Styles, and Techniques
• Musicology and Music History
• Performance Practice and Studies
• Race and Ethnicity in Music
• Sound Studies
• Browse content in Performing Arts
• Browse content in Philosophy
• Aesthetics and Philosophy of Art
• Epistemology
• Feminist Philosophy
• History of Western Philosophy
• Metaphysics
• Moral Philosophy
• Non-Western Philosophy
• Philosophy of Science
• Philosophy of Language
• Philosophy of Mind
• Philosophy of Perception
• Philosophy of Action
• Philosophy of Law
• Philosophy of Religion
• Philosophy of Mathematics and Logic
• Practical Ethics
• Social and Political Philosophy
• Browse content in Religion
• Biblical Studies
• Christianity
• East Asian Religions
• History of Religion
• Judaism and Jewish Studies
• Qumran Studies
• Religion and Education
• Religion and Health
• Religion and Politics
• Religion and Science
• Religion and Law
• Religion and Art, Literature, and Music
• Religious Studies
• Browse content in Society and Culture
• Cookery, Food, and Drink
• Cultural Studies
• Customs and Traditions
• Ethical Issues and Debates
• Hobbies, Games, Arts and Crafts
• Lifestyle, Home, and Garden
• Natural world, Country Life, and Pets
• Popular Beliefs and Controversial Knowledge
• Sports and Outdoor Recreation
• Technology and Society
• Travel and Holiday
• Visual Culture
• Browse content in Law
• Arbitration
• Browse content in Company and Commercial Law
• Commercial Law
• Company Law
• Browse content in Comparative Law
• Systems of Law
• Competition Law
• Browse content in Constitutional and Administrative Law
• Government Powers
• Judicial Review
• Local Government Law
• Military and Defence Law
• Parliamentary and Legislative Practice
• Construction Law
• Contract Law
• Browse content in Criminal Law
• Criminal Procedure
• Criminal Evidence Law
• Sentencing and Punishment
• Employment and Labour Law
• Environment and Energy Law
• Browse content in Financial Law
• Banking Law
• Insolvency Law
• History of Law
• Human Rights and Immigration
• Intellectual Property Law
• Browse content in International Law
• Private International Law and Conflict of Laws
• Public International Law
• IT and Communications Law
• Jurisprudence and Philosophy of Law
• Law and Politics
• Law and Society
• Browse content in Legal System and Practice
• Courts and Procedure
• Legal Skills and Practice
• Primary Sources of Law
• Regulation of Legal Profession
• Medical and Healthcare Law
• Browse content in Policing
• Criminal Investigation and Detection
• Police and Security Services
• Police Procedure and Law
• Police Regional Planning
• Browse content in Property Law
• Personal Property Law
• Study and Revision
• Terrorism and National Security Law
• Browse content in Trusts Law
• Wills and Probate or Succession
• Browse content in Medicine and Health
• Browse content in Allied Health Professions
• Arts Therapies
• Clinical Science
• Dietetics and Nutrition
• Occupational Therapy
• Operating Department Practice
• Physiotherapy
• Radiography
• Speech and Language Therapy
• Browse content in Anaesthetics
• General Anaesthesia
• Neuroanaesthesia
• Browse content in Clinical Medicine
• Acute Medicine
• Cardiovascular Medicine
• Clinical Genetics
• Clinical Pharmacology and Therapeutics
• Dermatology
• Endocrinology and Diabetes
• Gastroenterology
• Genito-urinary Medicine
• Geriatric Medicine
• Infectious Diseases
• Medical Toxicology
• Medical Oncology
• Pain Medicine
• Palliative Medicine
• Rehabilitation Medicine
• Respiratory Medicine and Pulmonology
• Rheumatology
• Sleep Medicine
• Sports and Exercise Medicine
• Clinical Neuroscience
• Community Medical Services
• Critical Care
• Emergency Medicine
• Forensic Medicine
• Haematology
• History of Medicine
• Browse content in Medical Dentistry
• Oral and Maxillofacial Surgery
• Paediatric Dentistry
• Restorative Dentistry and Orthodontics
• Surgical Dentistry
• Browse content in Medical Skills
• Clinical Skills
• Communication Skills
• Nursing Skills
• Surgical Skills
• Medical Ethics
• Medical Statistics and Methodology
• Browse content in Neurology
• Clinical Neurophysiology
• Neuropathology
• Nursing Studies
• Browse content in Obstetrics and Gynaecology
• Gynaecology
• Occupational Medicine
• Ophthalmology
• Otolaryngology (ENT)
• Browse content in Paediatrics
• Neonatology
• Browse content in Pathology
• Chemical Pathology
• Clinical Cytogenetics and Molecular Genetics
• Histopathology
• Medical Microbiology and Virology
• Patient Education and Information
• Browse content in Pharmacology
• Psychopharmacology
• Browse content in Popular Health
• Caring for Others
• Complementary and Alternative Medicine
• Self-help and Personal Development
• Browse content in Preclinical Medicine
• Cell Biology
• Molecular Biology and Genetics
• Reproduction, Growth and Development
• Primary Care
• Professional Development in Medicine
• Browse content in Psychiatry
• Addiction Medicine
• Child and Adolescent Psychiatry
• Forensic Psychiatry
• Learning Disabilities
• Old Age Psychiatry
• Psychotherapy
• Browse content in Public Health and Epidemiology
• Epidemiology
• Public Health
• Browse content in Radiology
• Clinical Radiology
• Interventional Radiology
• Nuclear Medicine
• Radiation Oncology
• Reproductive Medicine
• Browse content in Surgery
• Cardiothoracic Surgery
• Gastro-intestinal and Colorectal Surgery
• General Surgery
• Neurosurgery
• Paediatric Surgery
• Peri-operative Care
• Plastic and Reconstructive Surgery
• Surgical Oncology
• Transplant Surgery
• Trauma and Orthopaedic Surgery
• Vascular Surgery
• Browse content in Science and Mathematics
• Browse content in Biological Sciences
• Aquatic Biology
• Biochemistry
• Bioinformatics and Computational Biology
• Developmental Biology
• Ecology and Conservation
• Evolutionary Biology
• Genetics and Genomics
• Microbiology
• Molecular and Cell Biology
• Natural History
• Plant Sciences and Forestry
• Research Methods in Life Sciences
• Structural Biology
• Systems Biology
• Zoology and Animal Sciences
• Browse content in Chemistry
• Analytical Chemistry
• Computational Chemistry
• Crystallography
• Environmental Chemistry
• Industrial Chemistry
• Inorganic Chemistry
• Materials Chemistry
• Medicinal Chemistry
• Mineralogy and Gems
• Organic Chemistry
• Physical Chemistry
• Polymer Chemistry
• Study and Communication Skills in Chemistry
• Theoretical Chemistry
• Browse content in Computer Science
• Artificial Intelligence
• Computer Architecture and Logic Design
• Game Studies
• Human-Computer Interaction
• Mathematical Theory of Computation
• Programming Languages
• Software Engineering
• Systems Analysis and Design
• Virtual Reality
• Browse content in Computing
• Business Applications
• Computer Security
• Computer Games
• Computer Networking and Communications
• Digital Lifestyle
• Graphical and Digital Media Applications
• Operating Systems
• Browse content in Earth Sciences and Geography
• Atmospheric Sciences
• Environmental Geography
• Geology and the Lithosphere
• Maps and Map-making
• Meteorology and Climatology
• Oceanography and Hydrology
• Palaeontology
• Physical Geography and Topography
• Regional Geography
• Soil Science
• Urban Geography
• Browse content in Engineering and Technology
• Agriculture and Farming
• Biological Engineering
• Civil Engineering, Surveying, and Building
• Electronics and Communications Engineering
• Energy Technology
• Engineering (General)
• Environmental Science, Engineering, and Technology
• History of Engineering and Technology
• Mechanical Engineering and Materials
• Technology of Industrial Chemistry
• Transport Technology and Trades
• Browse content in Environmental Science
• Applied Ecology (Environmental Science)
• Conservation of the Environment (Environmental Science)
• Environmental Sustainability
• Environmentalist Thought and Ideology (Environmental Science)
• Management of Land and Natural Resources (Environmental Science)
• Natural Disasters (Environmental Science)
• Nuclear Issues (Environmental Science)
• Pollution and Threats to the Environment (Environmental Science)
• Social Impact of Environmental Issues (Environmental Science)
• History of Science and Technology
• Browse content in Materials Science
• Ceramics and Glasses
• Composite Materials
• Metals, Alloying, and Corrosion
• Nanotechnology
• Browse content in Mathematics
• Applied Mathematics
• Biomathematics and Statistics
• History of Mathematics
• Mathematical Education
• Mathematical Finance
• Mathematical Analysis
• Numerical and Computational Mathematics
• Probability and Statistics
• Pure Mathematics
• Browse content in Neuroscience
• Cognition and Behavioural Neuroscience
• Development of the Nervous System
• Disorders of the Nervous System
• History of Neuroscience
• Invertebrate Neurobiology
• Molecular and Cellular Systems
• Neuroendocrinology and Autonomic Nervous System
• Neuroscientific Techniques
• Sensory and Motor Systems
• Browse content in Physics
• Astronomy and Astrophysics
• Atomic, Molecular, and Optical Physics
• Biological and Medical Physics
• Classical Mechanics
• Computational Physics
• Condensed Matter Physics
• Electromagnetism, Optics, and Acoustics
• History of Physics
• Mathematical and Statistical Physics
• Measurement Science
• Nuclear Physics
• Particles and Fields
• Plasma Physics
• Quantum Physics
• Relativity and Gravitation
• Semiconductor and Mesoscopic Physics
• Browse content in Psychology
• Affective Sciences
• Clinical Psychology
• Cognitive Psychology
• Cognitive Neuroscience
• Criminal and Forensic Psychology
• Developmental Psychology
• Educational Psychology
• Evolutionary Psychology
• Health Psychology
• History and Systems in Psychology
• Music Psychology
• Neuropsychology
• Organizational Psychology
• Psychological Assessment and Testing
• Psychology of Human-Technology Interaction
• Psychology Professional Development and Training
• Research Methods in Psychology
• Social Psychology
• Browse content in Social Sciences
• Browse content in Anthropology
• Anthropology of Religion
• Human Evolution
• Medical Anthropology
• Physical Anthropology
• Regional Anthropology
• Social and Cultural Anthropology
• Theory and Practice of Anthropology
• Browse content in Business and Management
• Business Strategy
• Business Ethics
• Business History
• Business and Government
• Business and Technology
• Business and the Environment
• Comparative Management
• Corporate Governance
• Corporate Social Responsibility
• Entrepreneurship
• Health Management
• Human Resource Management
• Industrial and Employment Relations
• Industry Studies
• Information and Communication Technologies
• International Business
• Knowledge Management
• Management and Management Techniques
• Operations Management
• Organizational Theory and Behaviour
• Pensions and Pension Management
• Public and Nonprofit Management
• Strategic Management
• Supply Chain Management
• Browse content in Criminology and Criminal Justice
• Criminal Justice
• Criminology
• Forms of Crime
• International and Comparative Criminology
• Youth Violence and Juvenile Justice
• Development Studies
• Browse content in Economics
• Agricultural, Environmental, and Natural Resource Economics
• Asian Economics
• Behavioural Finance
• Behavioural Economics and Neuroeconomics
• Econometrics and Mathematical Economics
• Economic Systems
• Economic History
• Economic Methodology
• Economic Development and Growth
• Financial Markets
• Financial Institutions and Services
• General Economics and Teaching
• Health, Education, and Welfare
• History of Economic Thought
• International Economics
• Labour and Demographic Economics
• Law and Economics
• Macroeconomics and Monetary Economics
• Microeconomics
• Public Economics
• Urban, Rural, and Regional Economics
• Welfare Economics
• Browse content in Education
• Adult Education and Continuous Learning
• Care and Counselling of Students
• Early Childhood and Elementary Education
• Educational Equipment and Technology
• Educational Strategies and Policy
• Higher and Further Education
• Organization and Management of Education
• Philosophy and Theory of Education
• Schools Studies
• Secondary Education
• Teaching of a Specific Subject
• Teaching of Specific Groups and Special Educational Needs
• Teaching Skills and Techniques
• Browse content in Environment
• Applied Ecology (Social Science)
• Climate Change
• Conservation of the Environment (Social Science)
• Environmentalist Thought and Ideology (Social Science)
• Natural Disasters (Environment)
• Social Impact of Environmental Issues (Social Science)
• Browse content in Human Geography
• Cultural Geography
• Economic Geography
• Political Geography
• Browse content in Interdisciplinary Studies
• Communication Studies
• Museums, Libraries, and Information Sciences
• Browse content in Politics
• African Politics
• Asian Politics
• Chinese Politics
• Comparative Politics
• Conflict Politics
• Elections and Electoral Studies
• Environmental Politics
• European Union
• Foreign Policy
• Gender and Politics
• Human Rights and Politics
• Indian Politics
• International Relations
• International Organization (Politics)
• International Political Economy
• Irish Politics
• Latin American Politics
• Middle Eastern Politics
• Political Methodology
• Political Communication
• Political Philosophy
• Political Sociology
• Political Behaviour
• Political Economy
• Political Institutions
• Political Theory
• Politics and Law
• Public Administration
• Public Policy
• Quantitative Political Methodology
• Regional Political Studies
• Russian Politics
• Security Studies
• State and Local Government
• UK Politics
• US Politics
• Browse content in Regional and Area Studies
• African Studies
• Asian Studies
• East Asian Studies
• Japanese Studies
• Latin American Studies
• Middle Eastern Studies
• Native American Studies
• Scottish Studies
• Browse content in Research and Information
• Research Methods
• Browse content in Social Work
• Addictions and Substance Misuse
• Adoption and Fostering
• Care of the Elderly
• Child and Adolescent Social Work
• Couple and Family Social Work
• Developmental and Physical Disabilities Social Work
• Direct Practice and Clinical Social Work
• Emergency Services
• Human Behaviour and the Social Environment
• International and Global Issues in Social Work
• Mental and Behavioural Health
• Social Justice and Human Rights
• Social Policy and Advocacy
• Social Work and Crime and Justice
• Social Work Macro Practice
• Social Work Practice Settings
• Social Work Research and Evidence-based Practice
• Welfare and Benefit Systems
• Browse content in Sociology
• Childhood Studies
• Community Development
• Comparative and Historical Sociology
• Economic Sociology
• Gender and Sexuality
• Gerontology and Ageing
• Health, Illness, and Medicine
• Marriage and the Family
• Migration Studies
• Occupations, Professions, and Work
• Organizations
• Population and Demography
• Race and Ethnicity
• Social Theory
• Social Movements and Social Change
• Social Research and Statistics
• Social Stratification, Inequality, and Mobility
• Sociology of Religion
• Sociology of Education
• Sport and Leisure
• Urban and Rural Studies
• Browse content in Warfare and Defence
• Defence Strategy, Planning, and Research
• Land Forces and Warfare
• Military Administration
• Military Life and Institutions
• Naval Forces and Warfare
• Other Warfare and Defence Issues
• Peace Studies and Conflict Resolution
• Weapons and Equipment

• < Previous chapter
• Next chapter >

4 The Discovery of X Chromosome Inactivation

• Published: October 2013
• Cite Icon Cite
• Permissions Icon Permissions

This chapter considers how X inactivation, the mammalian method of dosage compensation, was discovered by Mary Lyon. Included in the discussion are her original observations, the prior revelations she needed before she could formulate the X inactivation hypothesis, and the evidence that gave it support. The basic steps in the process are presented. Also considered is why X inactivation is an ideal model to study the regulation of transcription and gene silencing in mammalian cells.

Signed in as

Institutional accounts.

• Google Scholar Indexing
• GoogleCrawler [DO NOT DELETE]

Personal account

• Sign in with email/username & password
• Get email alerts
• Save searches
• Purchase content
• Activate your purchase/trial code

Institutional access

• Sign in with a library card Sign in with username/password Recommend to your librarian
• Institutional account management
• Get help with access

Access to content on Oxford Academic is often provided through institutional subscriptions and purchases. If you are a member of an institution with an active account, you may be able to access content in one of the following ways:

IP based access

Typically, access is provided across an institutional network to a range of IP addresses. This authentication occurs automatically, and it is not possible to sign out of an IP authenticated account.

Sign in through your institution

Choose this option to get remote access when outside your institution. Shibboleth/Open Athens technology is used to provide single sign-on between your institution’s website and Oxford Academic.

• Click Sign in through your institution.
• Select your institution from the list provided, which will take you to your institution's website to sign in.
• When on the institution site, please use the credentials provided by your institution. Do not use an Oxford Academic personal account.
• Following successful sign in, you will be returned to Oxford Academic.

If your institution is not listed or you cannot sign in to your institution’s website, please contact your librarian or administrator.

Sign in with a library card

Enter your library card number to sign in. If you cannot sign in, please contact your librarian.

Society Members

Society member access to a journal is achieved in one of the following ways:

Sign in through society site

Many societies offer single sign-on between the society website and Oxford Academic. If you see ‘Sign in through society site’ in the sign in pane within a journal:

• Click Sign in through society site.
• When on the society site, please use the credentials provided by that society. Do not use an Oxford Academic personal account.

If you do not have a society account or have forgotten your username or password, please contact your society.

Sign in using a personal account

Some societies use Oxford Academic personal accounts to provide access to their members. See below.

A personal account can be used to get email alerts, save searches, purchase content, and activate subscriptions.

Some societies use Oxford Academic personal accounts to provide access to their members.

Viewing your signed in accounts

Click the account icon in the top right to:

• View your signed in personal account and access account management features.
• View the institutional accounts that are providing access.

Signed in but can't access content

Oxford Academic is home to a wide variety of products. The institutional subscription may not cover the content that you are trying to access. If you believe you should have access to that content, please contact your librarian.

For librarians and administrators, your personal account also provides access to institutional account management. Here you will find options to view and activate subscriptions, manage institutional settings and access options, access usage statistics, and more.

Our books are available by subscription or purchase to libraries and institutions.

• About Oxford Academic
• Publish journals with us
• University press partners
• What we publish
• New features  
• Open access
• Rights and permissions
• Accessibility
• Advertising
• Media enquiries
• Oxford University Press
• Oxford Languages
• University of Oxford

Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide

• Copyright © 2024 Oxford University Press
• Cookie settings
• Cookie policy
• Privacy policy
• Legal notice

This Feature Is Available To Subscribers Only

Sign In or Create an Account

This PDF is available to Subscribers Only

For full access to this pdf, sign in to an existing account, or purchase an annual subscription.

Lyonization

• Reference work entry
• First Online: 01 January 2016
• pp 1130–1131
• Cite this reference work entry

151 Accesses

Variegation in mammalian females as predicted by the Lyon hypothesis. In an XX mammalian female one of the X chromosomes remains in a condensed state (see Fig. L57 ). It replicates its DNA asynchronously and its genes are not transcribed after the blastocyst stage, 3.5–4.5 dpc in the trophectoderm and 5.5–6.5 dpc in the embryo cell initials of the female mouse. In the germline, the inactive X is reactivated at the time of beginning of meiosis (12.5–13.5 dpc; the average time of gestation in the mouse is 19 days). In the male, X-chromosomal inactivation is limited to the duration of meiosis, presumably to restrict deleterious recombination with the Y chromosome. After fertilization, and before implantation, inactivation recurs in the female. The inactive X chromosome moves to the perinuclear position during S phase where it is silenced (Zhang L-F et al 2007 Cell 129:693). The other X chromosome displays a more open structure and its gene content is expressed. The majority of the genes...

This is a preview of subscription content, log in via an institution to check access.

Access this chapter

• Available as PDF
• Read on any device
• Instant download
• Own it forever
• Durable hardcover edition
• Dispatched in 3 to 5 business days
• Free shipping worldwide - see info

Tax calculation will be finalised at checkout

Purchases are for personal use only

Institutional subscriptions

Rights and permissions

Reprints and permissions

Copyright information

© 2008 Springer Science+Business Media

About this entry

Cite this entry.

(2008). Lyonization. In: Encyclopedia of Genetics, Genomics, Proteomics and Informatics. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-6754-9_9661

Download citation

DOI : https://doi.org/10.1007/978-1-4020-6754-9_9661

Published : 16 July 2016

Publisher Name : Springer, Dordrecht

Print ISBN : 978-1-4020-6753-2

Online ISBN : 978-1-4020-6754-9

eBook Packages : Biomedical and Life Sciences Reference Module Biomedical and Life Sciences

Share this entry

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative

• Publish with us

Policies and ethics

• Find a journal
• Track your research

• Subscriber Services
• For Authors
• Publications
• Archaeology
• Art & Architecture
• Bilingual dictionaries
• Classical studies
• Encyclopedias
• English Dictionaries and Thesauri
• Language reference
• Linguistics
• Media studies
• Medicine and health
• Names studies
• Performing arts
• Science and technology
• Social sciences
• Society and culture
• Overview Pages
• Subject Reference
• English Dictionaries
• Bilingual Dictionaries

Recently viewed (0)

• Save Search

John Lackie

• Find at OUP.com
• Google Preview
• Share This Facebook LinkedIn Twitter

More on this Topic

• Lyon hypothesis in Oxford Dictionary of Biochemistry and Molecular Biology (2 ed.)
• Lyon hypothesis in Concise Medical Dictionary (8 ed.)
• View overview page for this topic

Related Content

Related overviews.

sex chromatin

• Publishing Information
• General Links for this Work
• A note on conventions
• Prefixes for SI Units
• Greek alphabet
• Single-letter and three-letter codes for amino acids
• Next Version

Lyon hypothesis  

The hypothesis, first advanced by Mary Lyon (1925–2014), that there is random inactivation of one of the two X chromosomes in cells of females. As a result, women are chimaeric for the products of the X chromosomes, which has been used as a means of demonstrating the monoclonal origin of papillomas and atherosclerotic plaques, using heterozygotes for isozymes of glucose-6-phosphate dehydrogenase.... ...

Access to the complete content on Oxford Reference requires a subscription or purchase. Public users are able to search the site and view the abstracts and keywords for each book and chapter without a subscription.

Please subscribe or login to access full text content.

If you have purchased a print title that contains an access token, please see the token for information about how to register your code.

For questions on access or troubleshooting, please check our FAQs , and if you can''t find the answer there, please contact us .

• Oxford University Press

PRINTED FROM OXFORD REFERENCE (www.oxfordreference.com). (c) Copyright Oxford University Press, 2023. All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single entry from a reference work in OR for personal use (for details see Privacy Policy and Legal Notice ).

date: 03 May 2024

• Cookie Policy
• Privacy Policy
• Legal Notice
• Accessibility
• [66.249.64.20|195.190.12.77]
• 195.190.12.77

Character limit 500 /500

Mary Lyon and the hypothesis of random X chromosome inactivation

Affiliation.

• 1 Institute of Medical Genetics, School of Medicine, Cardiff University, Cardiff, UK. [email protected]
• PMID: 21643983
• DOI: 10.1007/s00439-011-1013-x

The 50th anniversary of Mary Lyon's 1961 Nature paper, proposing random inactivation in early embryonic life of one of the two X chromosomes in the cells of mammalian females, provides an opportunity to remember and celebrate the work of those involved. While the hypothesis was initially put forward by Lyon based on findings in the mouse, it was founded on earlier studies, notably the work of Susumu Ohno; it was also suggested independently by Beutler and colleagues using experimental evidence from a human X-linked disorder, glucose-6-phosphate dehydrogenase deficiency, and has proved to be of as great importance for human and medical genetics as it has for general mammalian genetics. Alongside the hypothesis itself, previous cytological studies of mouse and human chromosomes, and the observations on X-linked mutants in both species deserve recognition for their essential role in underpinning the hypothesis of random X-inactivation, while subsequent research on the X-inactivation centre and the molecular mechanisms underlying the inactivation process represent some of the most outstanding contributions to human and wider mammalian genetics over the past 50 years.

Publication types

• Historical Article
• Biological Evolution*
• Developmental Biology / history*
• Genetics / history*
• History, 20th Century
• Research / history*
• X Chromosome Inactivation / genetics
• X Chromosome Inactivation / physiology*

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

• View all journals
• Explore content
• About the journal
• Publish with us
• Sign up for alerts
• Published: 05 May 1962

Twin Data in Support of the Lyon Hypothesis

• STEVEN G. VANDENBERG 1 ,
• VICTOR A. McKUSICK 2 &
• ANNE B. McKUSICK 2  

Nature volume  194 ,  pages 505–506 ( 1962 ) Cite this article

506 Accesses

15 Citations

Metrics details

THE Lyon hypothesis 1,2 suggests that in the XX mouse and human female one X chromosome is genetically inactive after a certain stage in embryogenesis; that this ‘inactive’ X chromosome forms the Barr body, which can be identified at about the sixteenth day in the human embryo; that it is a random proposition which of the two X chromosomes in a given cell becomes the genetically inactive one; that once it is decided which X chromosome is to be the genetically inactive one in a given cell all descendants of this cell abide by the decision and have the same X chromosome inactive; and that the germ cell line does not participate in this process of X chromosome differentiation. The hypothesis suggests a mechanism: (1) of dosage compensation for the ‘excess’ genetic material in females; (2) of the observed phenotypic variability in females heterozygous for X -borne recessive mutations. The hypothesis requires the existence, in heterozygous females, of two populations of cells with regard to a particular trait for which the female is heterozygous. Beutler 3 seems to have indirect evidence for such, in females heterozygous for glucose-6-phosphate dehydrogenase deficiency. All the genetic and cytological evidence supporting this attractive hypothesis 1–4 will not be reviewed here. Some further evidence in its support will, however, be presented.

This is a preview of subscription content, access via your institution

Access options

Subscribe to this journal

Receive 51 print issues and online access

185,98 € per year

only 3,65 € per issue

Buy this article

• Purchase on Springer Link
• Instant access to full article PDF

Prices may be subject to local taxes which are calculated during checkout

Similar content being viewed by others

Genome-wide association studies

Paternal microbiome perturbations impact offspring fitness

Multi-ancestry genome-wide association study of kidney cancer identifies 63 susceptibility regions

Lyon, M. F., Lancet , ii, 434 (1961).

Lyon, M. R., Nature , 190 , 372 (1961).

Article   ADS   CAS   PubMed   Google Scholar  

Beutler, E., Proc. U.S. Nat. Acad. Sci. , 48 , 9 (1962).

Article   ADS   CAS   Google Scholar  

McKusick, V. A., Quart. Rev. Biol. (in the press).

Clark, P. J., Amer. J. Hum. Genet. , 8 , 49 (1956).

CAS   PubMed   Google Scholar  

Sutton, H. E., de Lamadrid, E. Gil, and Ester, M. B., Amer. J. Hum. Genet. , 14 , 64 (1962).

Sutton, H. E., Vandenberg, S. G., and Clark, P. J., Amer. J. Hum. Genet. , 14 , 52 (1962).

Vandenberg, S. G., Amer. J. Hum. Genet. (in the press).

Download references

Author information

Authors and affiliations.

Department of Pediatrics, University of Louisville, Louisville, Kentucky

STEVEN G. VANDENBERG

Division of Medical Genetics, Department of Medicine, Johns Hopkins University, School of Medicine, Baltimore, 5, Maryland

VICTOR A. McKUSICK & ANNE B. McKUSICK

You can also search for this author in PubMed   Google Scholar

Rights and permissions

Reprints and permissions

About this article

Cite this article.

VANDENBERG, S., McKUSICK, V. & McKUSICK, A. Twin Data in Support of the Lyon Hypothesis. Nature 194 , 505–506 (1962). https://doi.org/10.1038/194505b0

Download citation

Issue Date : 05 May 1962

DOI : https://doi.org/10.1038/194505b0

Share this article

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative

This article is cited by

Environmental tracking by females.

• Del Thiessen

Human Nature (1994)

Steven G. Vandenberg (1915?1992)

• John C. Loehlin

Behavior Genetics (1993)

Twins, families, and the psychology of individual differences: The legacy of Steven G. Vandenberg

• Alan B. Zonderman

Behavior Genetics (1986)

By submitting a comment you agree to abide by our Terms and Community Guidelines . If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Quick links

• Explore articles by subject
• Guide to authors
• Editorial policies

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

IoT Standardization and Implementation Challenges

The 8 most brilliant fictional scientist we love (7/8), openmind books, scientific anniversaries, the lesser-known side of isaac asimov, featured author, latest book, mary lyon: the geneticist who discovered that women are (cellular) mosaics.

Sixty years ago, British geneticist Mary Frances Lyon (1925-2014) proposed a hypothesis stating that a specific inactivation process occurs in women’s sex chromosomes — and those of female mammals in general — transforming them into cellular mosaics. This hypothesis, which has been known ever since as lyonization, has been proven fully valid in our times, having led to interesting advances and discoveries.

LYONIZATION

At the end of the 1950s, it was discovered that the pair of sex chromosomes in males is comprised of a normally sized chromosome, the X chromosome inherited from the mother, and a very small chromosome, the Y, inherited from the father. In women, however, this pair consists of two X chromosomes, one from the father and one from the mother. It was then deduced that women have double the X chromosome genes than men, which is no small matter given that the X chromosome contains more than a thousand genes, whereas the Y has only about 75. Thus arose the enigma: are genes from both X chromosomes expressed within the female’s cells or is there some kind of compensation for women’s double dose of genes (compared to males).

Faced with this dilemma, Lyon first proposed that one of the somatic cell’s two X chromosomes in women — and in female mammals, in general — is inactivated in the phase when genes are expressed, in interphase1. Specifically what happens is that the inactivated X chromosome is completely condensed — a process that is called heterochromatinization — whereas the other X chromosome and the rest of the chromosomes are decondensed and expressed in RNA and proteins. The inactive X chromosome would be the origin of the sex chromatin or Barr body, a more darkly stained body observed in the nucleus of a female cell and which is absent in male cells. Even though female cells have a double dose of X-linked genes, the process of inactivation caused by heterochromatinization results in only one of the set — the one that has not been converted into heterochromatin — being active, thus compensating for the double dose in females, as compared to males who only have one X.

Secondly, Lyon proposed that inactivation occurs in the first phases of female development — in fact just two short hours from fertilization — and at random: in some cells the X chromosome inherited from the father is inactivated and in others it is the X chromosome from the mother. Thirdly, she sustained that once a specific X chromosome has been inactivated in a specific embryonic cell, all of the cells that originate from it will inherit said inactivation, with the result that all of the cells in the area of the adult body that this particular cell gave rise to will be inactive. This explains why organisms with coloration patches in the fur are usually female and not male. This is the case with tabby cats with black and orange patches on a white background. These cats would be heterozygous for the gene that determines the colors orange and black, which is located in the X chromosomes. The patches of color reflect the zones that have developed from cells that have inactivated one or the other of the X chromosomes. This is why in some zones one of the color alleles — the orange — is expressed and in other zones the other allele — the black — is expressed.

Therefore, and in conclusion, what has been known as lyonization causes mammalian females to be mosaics, where the genes of one or the other of the two X chromosomes carried in the cells are expressed, a phenomenon that does not happen in males because their cells contain only genes of a single X chromosome, in addition to the Y

REVOLUTIONARY GENETIC CONCEPTS RELATED TO LYONIZATION

Although Mary Lyon’s hypothesis about the inner workings of women’s (and mammalian females’) X chromosomes was at first met with some reservations, in later years it was generally accepted. Particularly because much of the research that her hypothesis prompted (some of it even conducted by her) received convincing genetic and cytologic results which supported the theory. Once confirmed, it represented the starting point for several discoveries, some of interest for theoretical biology and others with implications for clinical genetics.

Thirty years after Lyon’s initial work on the process, it was discovered2 that the chromosome X-inactivation in females is controlled by the very X chromosome to be inactivated. And as opposed to what normally happens, this is not because a protein comes from some other chromosome or from the same X chromosome. It happens because in the X chromosome where a gene is going to be inactivated, the Xist (for “X inactive specific transcript”) gene synthesizes a long RNA — it has more than 15,000 ribonucleotides — that in binding itself along the chromosome subjects the chromosome to the heterochromatinization process, inactivating it, and thus preventing the transcription process that occurs first with the messenger RNA and later with proteins. This was one of the first times that it was found that a long non-coding RNA (a non-protein coding transcript) could have a gene activation regulatory function, something that was later seen to occur in various biological situations.

Another exceptional genetic mechanism has been found to be related to female active X chromosomes. Specifically what happens in this chromosome is that another RNA (different from the previously mentioned one) is synthesized from the Xist gene. But this happens from the opposite strand of the gene’s double helix — and in the opposite direction — from that which is transcribed in the inactive chromosome. This RNA is called Tsix, Xist backwards. It is even longer than the Xist; it has 40,000 bases, and with its synthesis in the active X chromosome, it prevents the synthesis of the Xist RNA with the inactivating function3. It is also one of the first cases in which it was observed that two different RNAs were transcribed from a single gene: one in one direction of the gene’s double helix and another in the other direction, and where, in addition, one of the RNAs interferes with the other: if the Tsix impedes the Xist synthesis, it would be an anti-Xist.

CLINICAL IMPLICATIONS OF LYONIZATION

The phenomenon of lyonization that occurs during the development of women and mammalian females in general could also have clinical ramifications. Women are generally less likely than men to suffer diseases caused by gene mutations of the X chromosome. This is due to the fact that women have two X chromosomes, and if one carries a mutated gene, it can be substitute with the normal gene that comes from the other X chromosome. This does not occur in males because they only have one X chromosome. This is what happens with diseases like hemophilia, which involves hemorrhaging caused by a lack of a coagulation factors. In this case, men can be hemophiliacs due to a genetic mutation of their single X chromosome from which these factors are synthesized.  In contrast, although women can be carriers of the mutated gene in one of their X chromosomes, with the normal gene in the other X, enough coagulation proteins are produced to prevent hemorrhaging, event though it is only expressed in half of her cells and that only fifty percent of the normal coagulation factors are produced. This level is adequate to protect them from hemorrhaging, especially because the coagulation factors are released from the cells and circulate through the bloodstream where they can act upon the whole body.

But there are other situations in which the presence of an X chromosome with a functioning gene opposite a mutated gene in the other X chromosome of women does not protect them from the disease. This is what occurs, for example, in Rett syndrome, which is mainly prevalent in women with symptoms that include a serious cognitive disability — a severe form of autism — that becomes increasingly worse throughout the patient’s life4. This syndrome occurs as a result of a mutation in a gene in the X chromosome from which a protein is synthesized. The protein binds to the DNA in various locations and regulates the expression of many other genes. This occurs most of all in the brain. Whereas women with the mutation in both X chromosome genes or men with the mutation in their single X chromosome would not be viable, heterozygous (with one normal and one mutated gene) women are viable, but suffer from this syndrome. In this case what happens is that only half the brain cells of the patients express the normal gene — the cells that have inactivated the mutated X. But the other half, having inactivated the X with the normal gene, does not produce the protein. Half of the nerve cell production of the protein is not adequate for normal brain function.

PROSPECTS AND CONCLUSION

As we have said, the lyonization hypothesis has continued to prove valid through the present day. Though it continues to be a field of active research in many respects. First of all, much about the inactivation mechanism itself is being investigated: research on all the protein factors that interact with the RNA that react first, research on the effects of these factors on the DNA structure and the genes that are inactivated, etc. Secondly, there is ongoing research on the possible deviations in the process: there are cases in which inactivation does not occur randomly, but rather in some women activation occurs with a preference for either the paternal or maternal X chromosome; and research on the existence of genes that escape inactivation in the X chromosome that is heterochromatinized. All this research is also of clinical interest, for example, the latter two phenomena can play a role in certain illnesses and kinds of cancer. Likewise, v ery recently there has been investigation into to what degree men’s greater sensitivity to the coronavirus (SARS-CoV-19) could be related to their greater production of the cell membrane protein, ACE2 (Angio-tensin Converting Enzyme 2), which the virus uses to enter MRC-5 cells. The gene that controls this enzyme is located in the X chromosome, and if what happens is that men produce greater amounts of ACE2 than women and are therefore more susceptible to infections, the question is: How is this difference produced when Lyon’s hypothesis predicts that there should be equal production between the two sexes. Could this difference be due to the behavior of male hormones on the gene?

The pioneer behind this entire field of research, Mary F. Lyon, saw her hypothesis accepted and her work recognized as she was invited to join such important scientific societies such as the Royal Society (although she met with opposition) or the National Academy of Sciences in the U.S. She even lived to see her her name on a laboratory in the institute where she developed her work: the Mary Lyon Centre in Harwell, and in 2014 the establishment of the Mary Lyon Medal from the U.K. Genetics Society. However, she was not awarded the Nobel Prize, which many scientists claim she deserved for her revolutionary, comprehensive, and productive hypothesis.

Bibliography

• Lyon, MF. 1961.Gene Action in the X-chromosome of the mouse. Nature, 190:372-373. The first in a set of works in which the hypothesis is developed.
• Brown, C.J. et al.1991. A gene from the region of the human X inactive centre is expressed exclusively from the Inactive X chromosome. Nature, 349: 38-44.
• Lee JT et al.1999. Tsix, a gene antisense to Xist at the X inactivation center. Nat Genet, 21(4):400-4.
• Bienvenu, T. et al. 2000. MECP2 mutation account for most cases of typical forms of Rett syndrome. Hum. Mol. Genet. 9:1377-1384
• Sama, I.E et al. 14 May-2020. Circulating plasma concentration of Angiotensin Converting Enzyme 2 in men and women. Eur.Heart Journal. 41(19): 1810-1817.

Manuel Ruiz Rejón

Related publications.

• A Hidden Genetic Code?
• Jumping Genes: Disease and Health
• The Diseases That Hide in Our Genes

More about Science

Environment, leading figures, mathematics, scientific insights, more publications about manuel ruiz rejón, comments on this publication.

Morbi facilisis elit non mi lacinia lacinia. Nunc eleifend aliquet ipsum, nec blandit augue tincidunt nec. Donec scelerisque feugiat lectus nec congue. Quisque tristique tortor vitae turpis euismod, vitae aliquam dolor pretium. Donec luctus posuere ex sit amet scelerisque. Etiam sed neque magna. Mauris non scelerisque lectus. Ut rutrum ex porta, tristique mi vitae, volutpat urna.

Sed in semper tellus, eu efficitur ante. Quisque felis orci, fermentum quis arcu nec, elementum malesuada magna. Nulla vitae finibus ipsum. Aenean vel sapien a magna faucibus tristique ac et ligula. Sed auctor orci metus, vitae egestas libero lacinia quis. Nulla lacus sapien, efficitur mollis nisi tempor, gravida tincidunt sapien. In massa dui, varius vitae iaculis a, dignissim non felis. Ut sagittis pulvinar nisi, at tincidunt metus venenatis a. Ut aliquam scelerisque interdum. Mauris iaculis purus in nulla consequat, sed fermentum sapien condimentum. Aliquam rutrum erat lectus, nec placerat nisl mollis id. Lorem ipsum dolor sit amet, consectetur adipiscing elit.

Nam nisl nisi, efficitur et sem in, molestie vulputate libero. Quisque quis mattis lorem. Nunc quis convallis diam, id tincidunt risus. Donec nisl odio, convallis vel porttitor sit amet, lobortis a ante. Cras dapibus porta nulla, at laoreet quam euismod vitae. Fusce sollicitudin massa magna, eu dignissim magna cursus id. Quisque vel nisl tempus, lobortis nisl a, ornare lacus. Donec ac interdum massa. Curabitur id diam luctus, mollis augue vel, interdum risus. Nam vitae tortor erat. Proin quis tincidunt lorem.

The Astronomer who Looked Inside Trees

Do you want to stay up to date with our new publications.

Receive the OpenMind newsletter with all the latest contents published on our website

OpenMind Books

• The Search for Alternatives to Fossil Fuels
• View all books

About OpenMind

Connect with us.

• Keep up to date with our newsletter

• To save this word, you'll need to log in. Log In

Lyon hypothesis

Medical Definition of Lyon hypothesis

Dictionary entries near lyon hypothesis, cite this entry.

“Lyon hypothesis.” Merriam-Webster.com Medical Dictionary , Merriam-Webster, https://www.merriam-webster.com/medical/Lyon%20hypothesis. Accessed 3 May. 2024.

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Can you solve 4 words at once?

Word of the day.

See Definitions and Examples »

Get Word of the Day daily email!

Popular in Grammar & Usage

What’s the difference between ‘hillbilly’ and ‘redneck’, more commonly misspelled words, commonly misspelled words, how to use em dashes (—), en dashes (–) , and hyphens (-), absent letters that are heard anyway, popular in wordplay, 12 star wars words, the words of the week - may 3, 9 superb owl words, 10 words for lesser-known games and sports, your favorite band is in the dictionary, games & quizzes.

What is Lyon's hypothesis?

Lyon's hypothesis states that the phenotypic effect of the x chromosome is the same in the mammalian female which has two x chromosomes as it is in the male which has only one x chromosome. one out of two x chromosomes in females is inactivated early in embryonic development. it is called as the barr body. the barr body is highly condensed and does not have any phenotypic effect..

What is Munch's hypothesis?

What is hypothesis?

What is a hypothesis

DSpace JSPUI

Egyankosh preserves and enables easy and open access to all types of digital content including text, images, moving images, mpegs and data sets.

• IGNOU Self Learning Material (SLM)
• 04. School of Education (SOE)
• Master's Degree Programmes
• Master of Arts (Education) MA (Edu)
• Compulsory Courses
• MES-016 Educational Research
• Block-3 Research Design

Items in eGyanKosh are protected by copyright, with all rights reserved, unless otherwise indicated.

This map of neural pathways was generated with diffusion MRI, which Yvonne Lui uses to study athletes’ brains by analyzing the complex data with AI.

AI on the Brain

The human brain is an evolutionary wonder. With the help of machine learning, scientists at NYU Langone are finding ways to better comprehend and care for it

By Lindsy Van Gelder

As the repository of intelligence, the brain holds a kind of elevated position in the body. But like other organs, it’s vulnerable to illness and injury. Now neuroscientists at NYU Langone are using state-of-the-art tools—including artificial intelligence—to more accurately diagnose and treat brain tumors and to better understand and manage head trauma in athletes.

When dealing with a brain tumor, time is often of the essence. A glioblastoma, for example, can double in size in two weeks. One type of glioma—formed when the glial cells that support the nervous system multiply out of control—may call for a radically different treatment protocol than another, so the stakes are high when it comes to correctly classifying them. There are times that “it’s critical to be aggressive surgically,” says Daniel Orringer, a neurosurgeon at NYU Langone’s Brain and Spine Tumor Center at the Perlmutter Cancer Center. “In other cases, we know that the tumors may respond better to treatments like chemotherapy and radiation.”

Classifying these tumors cannot be done during surgery, since the differentiating genetic mutations are at the molecular level—and testing takes days or weeks in even the most advanced pathology lab. “What we have done in the past is give it our best guess . . . based on age, presenting symptoms, the way that the MRI looks, the way that the tumor looks in the operative field,” says Orringer, who is also an associate professor of neurosurgery and pathology at the Grossman School of Medicine. And hopefully the biopsy pathology results arriving later will validate the decisions made during surgery.

So Orringer developed an AI program called DeepGlioma that does away with the guesswork. Fresh harvested tissue goes into the system and the program creates an image. “We can see cells, we can see how they’re organized, we can see the shape of their nuclei. And there’s also some embedded chemical information,” he says. “From that dataset, the algorithm has been taught to associate certain features—whether those relate to the chemical makeup or the architectural features of the tissue—and integrate all the information it can absorb to make an accurate diagnosis.” And it only takes about 90 seconds. Now in clinical trials, DeepGlioma is completely portable and only requires an electrical outlet to mimic an advanced pathology lab. “We can kind of have our cake and eat it too,” says Orringer. “We get the molecular information in the time frame that allows us to apply that information in a way that’s most beneficial to the patient.”

Neurosurgeon Daniel Orringer created an AI device called DeepGlioma to help diagnose and treat brain cancer faster.

Innovating with AI has enabled another team at NYU Langone to gain fresh insight into the effects of head injuries on football players. It’s well established that repeated concussions can cause serious damage to a brain, but less is known about repeated head injuries that do not involve concussions, notes neuroradiologist Yvonne Lui, research vice chair in NYU Langone’s Department of Radiology. Lui has been studying athletes’ brains with a technique known as diffusion MRI, which uses water molecules to generate contrast on MRI images of brain tissue. The patterns of diffusion can yield information about the cellular-level composition of the tissue, but the technique also churns out massive amounts of data—which is where AI can be leveraged.

Lui had previously used standard statistical data analysis without AI to examine the brains of males who’d sustained concussions playing contact sports in college (football mostly, but also soccer and lacrosse) and contact-sports players who hadn’t been concussed. A third group of athletes in noncontact sports (baseball, basketball, cross country, and track) served as a control. The standard statistical methods allowed for comparisons of groups as a whole, and the researchers predictably found that the brains of the contact-sports athletes who’d had concussions differed from those of the noncontact control group. To their surprise, however, they also detected subtle statistical differences between the control group and the nonconcussed contact-sports group, which they reported in the American Journal of Neuroradiology .

Both nonconcussed groups are “high-performance athletes, they’re the same age, they’re eating the same foods, they’re going to the same colleges. You could argue that their brains should look the same. But they don’t,” says Lui. So her team more closely examined the brains of all the nonconcussed athletes with AI, which drills down into the data to compare not just groups but also individuals. The nonconcussed contact-sports athletes were presumed to have accumulated minor blows to the head, given their activities. The researchers fed data from some of those contact-sports players into an algorithm to train their computer to recognize the signs of repeated nonconcussive impacts. They reported in the Neuroradiology Journal that the machine had learned to distinguish between the brains of most of the remaining nonconcussed contact-sports players and members of the control group.

AI also identified which two of the many types of patterns generated by diffusion MRI were best at pinpointing the existence of these seemingly minor injuries. Whether repeated nonconcussive hits to the head can lead to the cognitive issues associated with multiple concussions is still a question, but Lui anticipates that her research will advance future diagnostic testing. She also hopes it proves how diffusion MRI and machine learning can illuminate small medical datasets. “Some people assume machine learning can only be useful in cases where you have millions of samples to train on, like self-driving cars and ChatGPT,” says Lui. “This paper is an example of using [it on a] small sample of subjects and finding reliable results.”

^ Back to top

Photos from top:  Yvonne Lui and Eyal Lotan; courtesy of NYU Langone