nonpenetrance

[nŏn-pĕnĭ-trəns]
n.
  1. The state in which a genetic trait although present in the appropriate genotype fails to manifest itself in the phenotype.
  2. The obscuring of genetic traits by nongenetic mechanisms.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.