Question on Genes Behind Comb Type (P p+ , R r+ , d+ Dv Dc , Bd+ bd)

Discussion in 'General breed discussions & FAQ' started by Gnarled Carrots, Oct 18, 2016.

  1. Gnarled Carrots

    Gnarled Carrots Out Of The Brooder

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    One of my chickens has a particularly weird comb (double rows of small spikes, much like a Carnation or a Buttercup, but much shorter like a Pea Comb). This got me wondering about what genes might be in the mix.

    A long way down the rabbit hole later!! there are a couple things about comb types that I'm not quite sure about.

    From my understanding, there are 4 genes that control comb type:
    • Pea Comb, P, p+
    • Rose Comb, R r+
    • Duplex Comb, d+, Dv, Dc
    • Breda, Bd+, bd

    Dominant Pea Comb, (P/P , r+/r+) or (P/p+ , r+/r+), creates a Pea Comb.
    Dominant Rose Comb, (p+/p+ , R/R) or (p+/p+ , R/r+), creates a Rose Comb.
    Any other combination of Pea and Rose Comb genes creates a Walnut Comb.
    The addition of Duplex Comb, (Dv), creates a V comb.
    The addition of Duplex Comb, (Dc), creates a cup-shaped comb.
    The addition of Breda, (Bd+), creates combless or very small combs.

    From my understanding, there are also 10 basic comb types:
    • Single Comb: (p+/p+ , r+/r+ , d+/d+ , Bd+/Bd+)
    • Rose Comb: (p+/p+ , R/R , d+/d+ , Bd+/Bd+) or (p+/p+ , R/r+ , d+/d+ , Bd+/Bd+)
    • Pea Comb: (P/P , r+/r+ , d+/d+ , Bd+/Bd+) or (P/p+ , r+/r+ , d+/d+ , Bd+/Bd+)
    • Walnut Comb: (any combination of Pea Comb genes that doesn't create a Pea Comb , any combination of Rose Comb genes that doesn't create a Rose Comb , d+/d+ , Bd+/Bd+)
    • Cushion Comb: (P/P , R/R , d+/d+ , Bd+/Bd+) or (P/p+ , R/r+ , d+/d+ , Bd+/Bd+)
    • Strawberry Comb: (P/??? , R/??? , d+/d+ , Bd+/Bd+)
    • V Comb: (r+/??? , p+/??? , Dv/Dv , Bd+/Bd+) or (r+/??? , p+/??? , Dv/d+ , Bd+/Bd+)
    • Carnation Comb: (r+/r+??? , p+/p+??? , Dv/Dv , Bd+/Bd+) or (r+/r+??? , p+/p+??? , Dv/d+ , Bd/+Bd+)
    • Buttercup Comb: (r+/r+??? , p+/p+??? , Dc/Dc , Bd+/Bd+) or (r+/r+??? , p+/p+??? , Dc/d+ , Bd+/Bd+)
    • Breda Comb: (any combination of Pea Comb genes , any combination of Rose Comb genes , any combination of Duplex Comb genes , bd/bd)

    What I'm confused on is what the base genes for other comb types are supposed to be (obviously, weird combinations of genes sometimes create combs that look similar for different reasons). I've marked the ones that I'm not exactly sure about.

    I'm also thinking that the homozygous Single, Rose, Pea, Cushion, and Breda Combs breed true. And the heterozygous Rose, Pea, Cushion, Carnation, and Buttercup Combs don't breed true. But what about the Strawberry, V, Carnation, and Buttercup Combs?
     
  2. Ridgerunner

    Ridgerunner Chicken Obsessed

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    I cannot answer your base questions, you are way ahead of me in that, but I did notice a basic mistake. The Pea gene is not a fully dominant gene, it is partially dominant. If you have (P/P, r/r) you will get a true Pea comb. But if you have (P/p, r/r) you get what I call a wonky Pea comb. You will definitely see the influence of the single Pea gene but the comb will look more like a cross between a single and pea. They can look a lot different, depending on what else is modifying them, but in general they are swollen but more upright. I need to get some photos of mine to show what I’m talking about but I’m making no promises on that being soon. I was thinking about doing that yesterday and didn’t do it.

    I’m sure there are other genes you didn’t mention, such as a gene to determine number of points on a comb that has points, whether the comb is upright or floppy, and who knows what else. There is always something else in chicken genetics. I’ll subscribe to this thread to see if someone really knowledgeable in comb genetics can help you.
     
  3. Gnarled Carrots

    Gnarled Carrots Out Of The Brooder

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    Feb 17, 2016
    Washington
    Thanks for the reply Ridgerunner!

    And sorry that I didn't specify. All of the heterozygous forms can be "wonky" and won't breed true. Chickens that are (P/p+ , R/r+) can appear to have a Cushion Comb, especially when they're young. Although oftentimes they'll develop ridges later. It might have something to do with how the genes develop when chickens go through puberty or after their first molt.

    I know that people talk about a gene that "smooths" out combs, but I can't find ANY research on it. Since the Cushion Comb can develop ridges in its heterozygous form, I'm thinking that ridging is probably controlled by the genes for Rose Comb, R, and Pea Comb, P. Chickens with recessive genes seem to have more ridging than those with dominant genes. The Single Comb has the most ridging and it's (r+/r+ , p+/p+).

    I also know that people talk about a gene that makes them larger, smaller, and floppy, but again I can't find any research on it. I'm thinking that maybe the interplay of dominant and recessive Breda Combless genes makes them larger and smaller. The homozygous recessive (bd/bd) creates virtually no comb. So maybe chickens with larger combs are (Bd+/Bd+) and chickens with smaller combs are (Bd+/bd)...?

    There's a chance that I've just fallen into a dead zone in research! The chicken genome wasn't sequenced until 2004 and it pretty much invalidated everything that we thought we knew about chicken genetics up until that point. They didn't even know that the Duplex Comb, D, was on a different loci until a couple years ago. A lot of papers on chicken genetics still don't even recognize Breda, Bd, as a separate gene.
     
  4. Ridgerunner

    Ridgerunner Chicken Obsessed

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    By definition the heterozygous forms won’t breed true. The genes are split and it’s random which one gets passed down. That has nothing to do with dominance. I’m not sure if that’s what you are implying or not. Reading your last line in your first post, I think that might be a question.

    When a chicken has two different genes at a gene pair, let’s use R/r, it’s purely random which gets passed down to its offspring. It may give an R or it may give an r. Say you have a male and a female, both with R/r and you breed them. About 25% of the offspring will wind up with R/R, half will have R/r, and the remaining will have r/r. Since it is random the percents won’t be exact but if you hatch enough chicks it will balance out.

    The Rose gene is supposed to be fully dominant. Whether it is R/R or R/r, you should get the full effect of the Rose gene. But with the example you gave, P/p, R/r, I’d expect the ridges you are seeing are from that partially dominant Pea gene being heterozygous, not homozygous.
     

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