UNIT 9.7 Detection of Nonrandom X Chromosome Inactivation

  1. Melissa M. Thouin,
  2. James M. Giron,
  3. Eric P. Hoffman

Published Online: 1 FEB 2003

DOI: 10.1002/0471142905.hg0907s35

Current Protocols in Human Genetics

Current Protocols in Human Genetics

How to Cite

Thouin, M. M., Giron, J. M. and Hoffman, E. P. 2003. Detection of Nonrandom X Chromosome Inactivation. Current Protocols in Human Genetics. 35:9.7:9.7.1–9.7.6.

Author Information

  1. Children's Research Institute, Washington, D.C.

Publication History

  1. Published Online: 1 FEB 2003
  2. Published Print: OCT 2002

This is not the most recent version of the article. View current version (21 JAN 2014)


This unit describes a PCR-based assay for distinguishing between the two X chromosomes in female cells and assessing the percentage of cells having each parental X chromosome active. Methylation of CpG residues in gene promoters is a major mechanism of transcriptional silencing. In mammalian female cells, hypermethylation is the way in which one X chromosome is inactivated. The X-inactivation assay described in the Basic Protocol relies on methylation sensitivity. In this unit, the highly polymorphic and therefore typically heterozygous (CAG)n region of the 5 end of the coding region of the human androgen receptor gene (HUMARA), at Xq11.2, is used to distinguish and compare the methylation activity of the X chromosomes.