Incomplete Dominant vs Complete Dominant vs Incomplete penetrant

Discussion in 'General breed discussions & FAQ' started by nicalandia, Aug 20, 2011.

  1. nicalandia

    nicalandia Overrun With Chickens

    Jul 16, 2009
    this post is dedicated to those that are working with dominant and recessive genes, below words are from Dr. Ron Okimoto a loved geneticist at the classroom forums..

    and here his words

    R. Okimoto :

    Most of the time you get what you expect. There are rare exceptions. Most of the time geneticist make the distinction between incompletely dominant and incompletely penetrant. Blue is an example that is incompletely dominant and sometimes it is incompletely penetrant.
    Complete dominance is when the heterozygotes look like the homozygotes. Rose comb is an example of this, you have a hard time telling the Rr birds from the RR by how they look. You can tell by other associated phenotypes like fertility, but you can't tell by how the comb looks. Incomplete dominance is when you can tell the heterozygotes from the homozygotes. Dominant white and blue are referred to as incompletely dominant for this reason. There are rare occasions, probably due to genetic background that the dominant alleles are not expressed. Hen feathering and muffs and beards are common examples, the incompletely dominant genes are usually expressed in the heterozotes, but there are a lot of times that you can't tell that the heterozygotes have the dominant gene. These cases are usually called incomplete penetrance. Sometimes (5 toes may be an example) birds that are homozygous for the dominant allele do not express the phenotype or only partially express it. These cases are also called incomplete penetrance.​

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