Lyonization

[lī′ə-nĭ-zāshən]
n.
  1. The phenomenon in which heterozygous females do not phenotypically express their X-linked recessive genotype or do so only randomly.X-inactivation
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.