Discussion in 'Colour Questions' started by Sallighted, Feb 23, 2011.

  1. Sallighted

    Sallighted Well-known Member

    Just a question for you colour buffs.... if I have a TB mare who is brown (pretty much as boring brown you can get) and as every single relation is listed as bay or brown I would be assuming she will be homozygous agouti (AA):confused: Know that obviously the best way to tell would be to test or wait another 8.5 months:p My guess is I will end up with a bay tobiano (dad is homo TT) which I am totally happy with but was also wishing/hoping that I might end up with black/white. Any guesses?
  2. mineees

    mineees Gold Member

    brown doesnt carry agouti,only horses with black points have agouti or a chestnut can carry agouti and not sure on the EE black(which is homozygous )...:)
  3. Sallighted

    Sallighted Well-known Member

    So if she is brown and dad is homozygous black what options do I have???:confused:
  4. Sallighted

    Sallighted Well-known Member

    Also in the colour calculator there is not option for brown only bay or black... which should I be choosing????
  5. mineees

    mineees Gold Member

    hmmm you are correct...

    But, the way genetics works a homozygous black has to pass on the black gene(E)the brown could pass on a red(e) or a black gene(E).There for unless your homozygous black is carrying agouti,you will only get a Ee(brown) or EE(Black).Dad being homozygous tobiano, you will get a tobiano black or brown foal...Hope this makes sense...we are not sure if a EE (black) can carry agouti without showing it...
  6. mineees

    mineees Gold Member

    is dad homozygous black and homozygous tobiano, if hes not homo black,he can put in a red gene(e) and if mum puts in a red gene (e) you will get a chestnut.
  7. Sallighted

    Sallighted Well-known Member

    So let me get this right she would be Ee for a colour base (ie. one black and one red) and no agouti so aa???

    So my options for offspring would be EE (black) and Ee (brown) taking into consideration that we are assuming the sire is also Agouti negative aa???
  8. Tintara

    Tintara Well-known Member

    Black does not carry agouti; brown and bay do because both these colours have black pigment restricted in some way ie it is not uniformly spread across their entire body. It is now widely accepted that there are probably 2 different versions of agouti - brown which is relatively weak and only removes black pigment from the soft spots and bay which is much stronger and can restrict black pigment entirely to the points.

    If your mare only carries one copy of agouti you could end up with brown or black tobiano. If she carries two copies of 'brown' agouti you will end up with brown tobiano; if she carries a copy of 'brown' agouti and a copy of 'bay' agouti you could get either brown or bay tobiano. Unfortunately there is no test yet available to determine brown or bay agouti but there are plenty of people working on it.

    Note I'm assuming here that there is no red in the equation.
  9. Sallighted

    Sallighted Well-known Member

    Thanks Tintara :)
    Last edited: Feb 24, 2011
  10. Kate O

    Kate O New Member

    There has been a test for brown agouti around for a couple years now at Pet DNA services >> Pet DNA Services of AZ - Equine Services

    If you were to test for agouti at Animal Genetics or UC Davis, where they test for the absence of agouti (a), then any horses where they couldn't find the 'absence', would come back as carrying agouti - which is correct, but it doesn't specify which agouti, it just lists it as 'A'. Whereas Pet DNA will tell you if the horse is Black (a), Brown (At), or Bay (A).
  11. HarleyQH

    HarleyQH Well-known Member

    Thanks Kate for clarifying agouti for us. :) I have wondered myself the difference of At and A, now I know :)

    Because a parent is Bay or brown and its parents were brown /Bay it doesn't mean your horse is homozygous for agouti. If it is hetrozygous it has a 50% chance of throwing the agouti as only half the gene Aa is passed on. If sire is a non agouti carrier then foal has 50/50 chance of being brown or bay depending on the agouti ie brown At or A. A homozygous agouti horse looks the same as a hetro so testing is your only option. Even waiting for foal doesn't tell you here agouti geneotype.
    Hope I haven't confused anyone

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