X chromosome inactivation
This PowerPoint file contains a number of slides that may be useful for teaching of
genetics concepts.
You may use these slides and their contents for non-commercial educational purposes.
This presentation includes:
• A diagram illustrating X inactivation
• A slide showing a Barr body with inactive X chromatin
• Clinical implications of X inactivation, with questions for consideration.
© 2009 NHS National Genetics Education and Development Centre
Genetics and Genomics for Healthcare
www.geneticseducation.nhs.uk
X-inactivation is an
epigenetic process.
Because of X-inactivation
every female is a mosaic of
cell lines with different
active X chromosomes
Fig. 7.4 ©Scion Publishing Ltd
© 2009 NHS National Genetics Education and Development Centre
Genetics and Genomics for Healthcare
www.geneticseducation.nhs.uk
Barr body - inactive X chromatin
© 2009 NHS National Genetics Education and Development Centre
Genetics and Genomics for Healthcare
www.geneticseducation.nhs.uk
Clinical implications of X-Inactivation
Questions for consideration:
• Why is it difficult to determine if a gene is at the tip of Xp/Yp through
linkage studies?
• Why don’t all women have features of Turner syndrome if one X
chromosome is inactivated?
• Why are there clinical effects associated with additional X chromosomes?
• Why was a buccal smear used for confirming whether an athlete was a
male or a female?
© 2009 NHS National Genetics Education and Development Centre
Genetics and Genomics for Healthcare
www.geneticseducation.nhs.uk
Clinical implications of X-Inactivation
Questions for consideration (cont):
• Why do women have twice the levels of steroid sulphatase as men?
• Why do women who are carriers for X-linked ectodermal dysplasia have an
abnormal sweat gland pattern?
• Why do some carriers of Duchenne muscular dystrophy have very high
levels of CK whilst others have very low levels?
• Why do some women show signs of Duchenne muscular dystrophy?
© 2009 NHS National Genetics Education and Development Centre
Genetics and Genomics for Healthcare
www.geneticseducation.nhs.uk