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.

Fig. 7.4 ©Scion Publishing Ltd 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

Barr body - inactive X chromatin

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?

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?