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Posted: Thu Feb 14, 2002 2:05 pm
by Nancy Bartol
Is there a difference between variable penetrance and incomplete penetrance?

Posted: Fri Feb 15, 2002 2:36 pm
by Ned Patterson DVM

The technical terms that most geneticists use are Variable Expressivity and Incomplete Penetrance. Both of these refer situations in which a disease is caused by a defect in one gene but other factors (other genes and sometimes the environment modify what clinical signs are seen.) Variable expressivity usually refers to cases in which all affected animals show some signs but the signs might vary from mild to severe. Incomplete penetrance refers to an extreme of variable expressivity in which the expressed results of the disease are so mild as to be undetectable in some individuals, and thus some individual with the genetic defect appear normal.

So, in summary, incomplete penetrance is an extreme form of variable expressivity, but does specifically imply that some individuals with the defect show no detectable signs.

[This message has been edited by Ned Patterson DVM (edited 02-15-2002).]

Posted: Tue Feb 26, 2002 12:06 pm
by Nancy Bartol
Are there any studies showing that outcrossing (to a different breed) has produced a more extreme expression of a disorder than that typically found in a purebred breed?

If so, what's the genetics behind such an occurrence and could variable expressivity/complete penetrance come into play here?

Thanks very much for your comments.